Your veterinarian heard a heart murmur during your dog's annual exam, and terms like "myxomatous mitral valve disease" or "leaky valve" were introduced. The immediate questions are: what does this mean, how urgent is it, what are the progression stages, and do we really need to run an echocardiogram?

This article provides an in-depth clinical guide to canine myxomatous mitral valve disease (MMVD) — the most common acquired heart disease in dogs. We will examine the ACVIM 2019 staging system, review the landmark EPIC clinical trial numbers, and explore the latest real-world primary-care evidence from the 2025 VetCompass study, helping you make informed diagnostic and treatment decisions alongside your veterinarian.

Scenario Question

My 10-year-old Cavalier King Charles Spaniel has a new heart murmur. The veterinarian said it is likely "mitral valve disease" and mentioned starting a medication called pimobendan. What does this mean, how fast does the disease progress, how long will she live, and do I really need to pay for an expensive echocardiogram?

Direct Answer

Myxomatous mitral valve disease (MMVD) is a degenerative thickening of the mitral valve that causes blood to leak backward, eventually forcing the heart to enlarge and remodel. It is the most common cardiac disease in dogs, particularly older small breeds. Under the ACVIM 2019 consensus guidelines, MMVD is staged A through D, and treatment decisions are driven strictly by these stages rather than the mere presence of a murmur.

For most dogs, the disease progresses slowly over years. The landmark EPIC trial demonstrated that starting pimobendan at Stage B2 (where heart enlargement is visible but before heart failure occurs) delays the onset of congestive heart failure (CHF) or cardiac death by a median of 462 days (roughly 15 months). Furthermore, a 2025 VetCompass study of 928 real-world UK primary-care dogs found that prescribing pimobendan after a grade IV/VI murmur was associated with a significant reduction in 5-year CHF risk (34.1% vs 56.3% in untreated dogs) and a doubling of 5-year survival rates (19.8% vs 9.6%). Crucially, this real-world benefit was observed even in dogs that did not receive a formal echocardiogram, indicating that in cases where specialized imaging is financially out of reach, initiating treatment based on a clear clinical murmur is a reasonable and evidence-backed decision.

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What is myxomatous mitral valve disease, and why is the mitral valve leaking?

To understand myxomatous mitral valve disease (MMVD) — also known as chronic degenerative valvular disease (CDVD) or endocardiosis — we must look at the basic anatomy of the canine heart. The heart is divided into four chambers: the right atrium and ventricle, which pump blood to the lungs, and the left atrium and ventricle, which receive oxygenated blood from the lungs and pump it to the body.

The mitral valve is a two-leaflet valve located between the left atrium and the left ventricle. Its job is to act as a one-way door. When the left ventricle contracts (systole) to pump blood to the body, the mitral valve leaflets close tightly, preventing blood from flowing backward into the left atrium.

In dogs with MMVD, a degenerative process breaks down the normal connective tissue structure within the valve leaflets and the supporting chordae tendineae (the "heart strings" that anchor the valve leaflets). The leaflets undergo myxomatous degeneration: they accumulate abnormal glycosaminoglycans, causing the leaflets to become thick, lumpy, weakened, and distorted.

Because the leaflets can no longer form a tight seal, a portion of the blood leaks backward into the left atrium during ventricular contraction. This backward leakage is called mitral regurgitation. The turbulent blood flow passing through this leaky valve creates the whooshing sound heard through a stethoscope — a heart murmur.

As the disease progresses, the volume of regurgitant blood increases. To accommodate this extra volume, the left atrium must stretch and enlarge. Eventually, the left ventricle also enlarges to maintain adequate cardiac output to the body. This structural modification is known as cardiac remodeling. If the remodeling cannot keep pace with the volume overload, pressure inside the left atrium rises, causing fluid to back up into the pulmonary vessels and leak into the lung tissue. This state is called pulmonary edema, which is the hallmark of congestive heart failure.

MMVD is primarily an age-related, degenerative condition. It is not caused by infection or lack of exercise. It is highly prevalent in small-to-medium breed dogs, and genetics play a major role, particularly in certain breeds where the disease appears earlier and progresses more rapidly.

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How is MMVD diagnosed: murmur, X-ray, echocardiogram, and NT-proBNP

Diagnosing and managing MMVD requires a multi-step workup. A veterinarian cannot determine the stage of heart disease or prescribe the correct medications based on listening to the heart alone. The following diagnostic tools are used to build a complete picture of the heart's size and function:

1. Cardiac Auscultation (The Stethoscope Exam)

Auscultation is the starting point. The veterinarian listens for the presence of a murmur, determines its location (typically loudest on the left side of the chest over the apex of the heart), and assigns it a grade from I to VI based on intensity:

• Grade I: Very soft, heard only after listening carefully in a quiet room.
• Grade II: Soft, but easily heard immediately upon placing the stethoscope.
• Grade III: Moderate intensity; easily heard and as loud as the normal heart sounds.
• Grade IV: Loud murmur, louder than normal heart sounds, but without a physical vibration (thrill) felt on the chest wall.
• Grade V: Very loud murmur, easily heard, and accompanied by a palpable physical vibration (precordial thrill) felt when touching the chest.
• Grade VI: Exceptionally loud murmur that can be heard even when the stethoscope is lifted slightly off the chest wall, with a strong physical thrill.

While murmur intensity does not correlate perfectly with the severity of heart disease in all species, in canine MMVD, louder murmurs (Grade III and above) are more likely to be associated with significant cardiac remodeling. If a veterinarian hears a new murmur or notes that a previously documented murmur has increased in grade (e.g., from a Grade II to a Grade IV), further diagnostics are indicated. For more information on the initial detection of heart murmurs, see our guide on heart murmur in dogs.

2. Thoracic Radiographs (Chest X-rays)

Chest X-rays are critical for assessing the overall size of the heart and, crucially, checking the lungs for fluid (pulmonary edema). X-rays allow the veterinarian to:

• Measure the Vertebral Heart Score (VHS): A standardized method of measuring the length and width of the heart relative to the dog's thoracic vertebrae. A normal VHS in most breeds is between 8.5 and 10.5. A VHS greater than 11.5 is a strong indicator of cardiomegaly (heart enlargement).
• Assess for left atrial enlargement: Look for the characteristic "backsteep" or "double density" sign on the lateral view and "splitting" of the mainstem bronchi on the ventrodorsal view.
• Rule in or rule out congestive heart failure: If pulmonary edema is present (visible as patchy, increased density in the lung fields, typically in the hilar or caudodorsal regions), the dog has progressed to active heart failure.

3. Echocardiography (Cardiac Ultrasound)

An echocardiogram performed by a veterinary cardiologist is the gold standard for diagnosing MMVD. Ultrasound allows direct, real-time visualization of the heart chambers, valve leaflets, and blood flow. It is the only test that can definitively confirm the diagnosis and measure the exact parameters required for staging. Specifically, the cardiologist will measure:

• LA/Ao Ratio: The ratio of the left atrial diameter to the aortic root diameter. A normal ratio is less than 1.5. A ratio of 1.6 or greater indicates significant left atrial enlargement.
• LVIDd (Normalized): The left ventricular internal diameter in diastole, normalized to the dog's body weight. A normalized LVIDd of 1.7 or greater indicates significant left ventricular enlargement.
• Mitral valve leaflet structure (prolapse, thickening) and the presence of jet regurgitation using color Doppler.

4. NT-proBNP (Cardiac Biomarker)

N-terminal pro-B-type natriuretic peptide (NT-proBNP) is a blood test that measures a hormone released by heart muscle cells when they are stretched or under increased pressure.

• It is useful as a screening tool. A normal NT-proBNP value (typically < 900 pmol/L) suggests that significant heart enlargement is unlikely, meaning the dog is likely in Stage B1 rather than B2.
• An elevated NT-proBNP suggests that cardiac remodeling is occurring, indicating that an echocardiogram is highly recommended to check for Stage B2.
• It is also useful in emergency settings to help differentiate whether a dog with respiratory distress is dyspneic due to heart failure (where NT-proBNP will be highly elevated, often > 1500 pmol/L) or primary airway disease.

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The ACVIM 2019 stages (A, B1, B2, C, D) and why the stage drives every decision

In 2019, the American College of Veterinary Internal Medicine (ACVIM) published updated consensus guidelines for the diagnosis and treatment of MMVD in dogs (Keene et al., 2019). These guidelines classify the disease into five distinct stages, from at-risk to refractory heart failure. The stage of the disease — not the presence of the murmur or the dog's age — dictates the medical management and monitoring plan.

ACVIM Stage	Description	Diagnostic Criteria	Standard Management	Monitoring Interval
Stage A	At-Risk: Dogs predisposed to MMVD but currently have no structural heart disease, no murmur, and no clinical signs.	At-risk breed (e.g., Cavalier King Charles Spaniel, Dachshund, Poodle) with normal cardiac auscultation.	No drug treatment. No dietary restrictions. Regular annual screening auscultation.	Annually during routine checkups.
Stage B1	Preclinical (No Remodeling): Dogs with a documented heart murmur of MMVD but no radiographic or echocardiographic evidence of cardiac remodeling/enlargement.	Murmur present. Normal heart size on X-ray (VHS <= 10.5) and echo (LA/Ao < 1.6, LVIDd < 1.7).	No drug treatment. No dietary changes. Regular monitoring to detect progression to Stage B2.	Re-evaluate in 6–12 months with auscultation and blood pressure; repeat imaging if murmur gets louder.
Stage B2	Preclinical (With Remodeling): Dogs with a murmur and significant cardiac enlargement, but have never shown signs of congestive heart failure.	Murmur present (typically >= Grade III/VI). Echo shows LA/Ao >= 1.6 AND LVIDd >= 1.7. Radiographs show VHS >= 11.5 (or breed-adjusted elevation).	Initiate Pimobendan as directed by your veterinarian. Mild dietary sodium restriction. Avoid high-salt treats.	Re-evaluate in 4–6 months with thoracic radiographs, blood pressure, and renal panel.
Stage C	Congestive Heart Failure (CHF): Dogs with past or current clinical signs of heart failure (coughing, tachypnea, dyspnea, exercise intolerance) caused by MMVD.	Murmur present. Active pulmonary edema on radiographs, or history of CHF successfully controlled with medication.	Quadruple Therapy: 1. Pimobendan (under veterinary guidance) 2. Furosemide (diuretic to clear edema) 3. ACE Inhibitor (e.g., enalapril or benazepril) 4. Spironolactone (aldosterone antagonist)	Re-evaluate 7–14 days after starting/adjusting CHF meds, then every 2–4 months. Home breathing rate monitoring.
Stage D	Refractory CHF: Dogs with end-stage MMVD whose clinical signs of CHF are refractory to standard therapeutic doses of Stage C medications.	Murmur present. Recurrent pulmonary edema or ascites despite high doses of diuretics, pimobendan, and standard adjunctive therapies.	Advanced specialist care: switch standard diuretic to torsemide, add additional vasodilators (e.g., sildenafil for pulmonary hypertension), mechanical fluid removal (centesis).	Intensive, frequent monitoring. Focus shifts to palliative care and quality-of-life assessments.

The Critical Transition: Stage B1 versus Stage B2

The most important clinical decision in preclinical MMVD is distinguishing between Stage B1 and Stage B2.

• Stage B1 dogs do not benefit from starting medication. Large clinical trials have shown that drugs started in B1 do not delay the onset of heart disease or extend life. Starting drugs too early increases financial cost and subjects the dog to potential side effects without benefit.
• Stage B2 dogs derive massive benefit from starting pimobendan. Because the heart has begun to enlarge under the volume overload, intervention is required. Starting pimobendan at this stage significantly extends the asymptomatic phase, buying the dog more time before developing heart failure.

To confirm a dog has reached Stage B2, the ACVIM guidelines require meeting three specific criteria:

1. A heart murmur intensity of Grade III/VI or louder.
2. An echocardiographic LA/Ao ratio of 1.6 or greater (measured in early diastole).
3. An echocardiographic normalized LVIDd of 1.7 or greater.
4. Supporting radiographic evidence of cardiomegaly, typically defined as a VHS of 11.5 or greater.

If the dog does not meet these criteria, they remain in Stage B1 and should be monitored rather than medicated. If they meet these criteria, they are in Stage B2, and pimobendan should be started.

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The EPIC trial: what pimobendan actually does (and the 15-month result)

The medical management of Stage B2 MMVD was revolutionized by the publication of the EPIC Trial (Evaluation of Pimobendan in Dogs with Cardiomegaly caused by Preclinical Mitral Valve Disease) in 2016 (Boswood et al., 2016).

Study Design

The EPIC trial was a prospective, multi-center, randomized, double-blind, placebo-controlled clinical study. It evaluated 360 dogs across 11 countries. To be enrolled, dogs had to be:

• At least 6 years of age.
• Weigh between 4.1 and 15 kg.
• Have a documented MMVD murmur of Grade III/VI or louder.
• Have echocardiographic and radiographic evidence of Stage B2 cardiac enlargement (LA/Ao >= 1.6, normalized LVIDd >= 1.7, and VHS > 10.5).

The dogs were randomly assigned to receive either pimobendan (prescribed at standard label doses) or a matching placebo.

Landmark Results

The study was designed to run for several years, but it was terminated early by the independent data safety monitoring board because the interim analysis revealed a clear, overwhelming benefit in the pimobendan-treated group. The primary endpoint was a composite of the onset of congestive heart failure, cardiac-related death, or euthanasia.

The key findings were:

• Delay of Heart Failure: Pimobendan delayed the primary endpoint of CHF or death by a median of 462 days (15.2 months) compared to the placebo. The median time to the primary endpoint was 1,228 days for the pimobendan group versus 766 days for the placebo group.
• Survival Benefit: The overall survival time was significantly longer in the pimobendan group. The median overall survival was 1,059 days (34.8 months) for dogs receiving pimobendan, compared to 902 days (29.6 months) for dogs receiving the placebo.
• Quality of Life: Dogs in the pimobendan group remained in the preclinical, asymptomatic phase significantly longer, preserving their quality of life.
• Safety Profile: There was no significant difference in the rate or type of adverse events between the pimobendan and placebo groups, confirming that the drug is highly tolerated in dogs with cardiac remodeling.

Pimobendan (brand name Vetmedin) acts as an inodilator. It has two primary mechanisms of action:

1. Positive Inotropy: It increases the contractility (pumping strength) of the heart muscle by sensitizing cardiac myofibrils to calcium, without increasing intracellular calcium levels (which avoids triggering arrhythmias).
2. Vasodilation: It relaxes vascular smooth muscle, causing systemic arterial and venous vasodilation. This reduces both preload (the volume of blood returning to the heart) and afterload (the resistance the heart must pump against), making it easier for the heart to pump blood forward and reducing the volume of blood leaking backward through the mitral valve.

The EPIC trial established a firm clinical standard: once a dog is confirmed to be in Stage B2, pimobendan is the drug of choice to delay the onset of heart failure. For a detailed breakdown of the pharmacology and adverse-event reports associated with this drug, see our Vetmedin (pimobendan) side effects analysis.

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Real-world evidence: what the 2025 VetCompass study of 928 dogs changed

While the EPIC trial was a gold-standard randomized controlled trial (RCT), RCTs take place in highly controlled environments with strict inclusion criteria and expert monitoring. They do not always represent standard veterinary practice, where financial constraints, access to cardiologists, and patient compliance vary.

To address this, a landmark study was published in 2025 by the Royal Veterinary College's (RVC) VetCompass program (Pegram et al., 2025). The study used causal inference methodology to emulate the EPIC trial design using real-world electronic health record (EHR) data from primary-care veterinary clinics in the United Kingdom.

Study Methodology

The researchers identified a cohort of 928 dogs under primary veterinary care in the UK. The inclusion criteria mirrored the EPIC trial:

• Dogs were at least 6 years of age.
• Weighed 15 kg or less.
• Had a documented Grade IV/VI or louder heart murmur (indicating presumed preclinical MMVD).
• Of the 928 dogs, 178 (19.2%) were prescribed pimobendan within 6 months of the murmur detection, while 750 (80.8%) were not prescribed pimobendan.

The researchers used inverse probability of treatment weighting (IPTW) to balance the demographic, clinical, and diagnostic differences between the treated and untreated groups, allowing them to draw causal conclusions from observational data.

Key Real-World Findings

The VetCompass study strongly validated the findings of the EPIC trial in a real-world setting, showing even more pronounced differences in survival and heart failure risk over a 5-year follow-up period:

• Congestive Heart Failure Risk: Over 5 years, the risk of developing congestive heart failure was 34.1% in the pimobendan-treated group, compared to 56.3% in the untreated group.
• Overall Survival Rate: The 5-year survival rate was 19.8% for dogs prescribed pimobendan, compared to only 9.6% for those that were not.
• Days of Health Gained: Dogs prescribed pimobendan spent an average of 311 fewer days suffering from or lost to congestive heart failure over the 5-year study period compared to untreated dogs.
• Mean Survival Time: The adjusted mean survival time was 1,051 days for the pimobendan group, compared to 905 days for the untreated group — an adjusted difference of 146 days in a primary-care cohort.

The Demographic Profile

The VetCompass data provided valuable insights into which dogs are most affected by MMVD in general practice. In this cohort of small dogs with loud murmurs:

• The Cavalier King Charles Spaniel was the single most common breed, accounting for 33.7% of the pimobendan group and 32.1% of the untreated group.
• Other highly represented breeds included the King Charles Spaniel, Chihuahua, Shih Tzu, Jack Russell Terrier, Bichon Frise, Yorkshire Terrier, and Miniature Schnauzer.
• The median age of dogs prescribed pimobendan was 9.9 years, compared to 10.6 years for those not prescribed.

The Diagnostic and Financial Gap

The most striking findings of the VetCompass study related to veterinary practice patterns and financial access:

• Echocardiography Rates: An echocardiogram was performed in only 53.9% of the dogs that received pimobendan. In the untreated group, only 7.3% of dogs underwent an echocardiogram.
• Insurance Status: Insured dogs were nearly twice as likely to be prescribed pimobendan (40.4% of the treated group was insured, compared to only 21.6% of the untreated group).

This highlights a major real-world barrier: the vast majority of primary-care dogs with heart murmurs never receive an echocardiogram, often due to the cost of specialist referral (typically $800 to $1,500) or geographic unavailability. Because the ACVIM guidelines strictly require an echocardiogram to diagnose Stage B2, many veterinarians have historically hesitated to prescribe pimobendan without one, leaving a large portion of at-risk dogs untreated.

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What an echocardiogram is for — and whether you can treat MMVD without one

The difference between the ACVIM guidelines (which mandate an echocardiogram) and real-world practice (where 46% of treated dogs and 92% of untreated dogs did not get one) raises a crucial clinical question: Is an echocardiogram always mandatory, or can a veterinarian safely start pimobendan based on a heart murmur and chest X-rays alone?

The Value of the Echocardiogram

An echocardiogram is undoubtedly the best diagnostic tool. It provides:

1. Definitive Diagnosis: It rules out other causes of murmurs, such as tricuspid valve disease, dilated cardiomyopathy, congenital defects (VSD, PDA), or subaortic stenosis. For a comparison of valvular disease and myocardial disease, read our guide on dilated cardiomyopathy in dogs.
2. Precise Staging: It measures the exact LA/Ao ratio and normalized LVIDd. This prevents starting medications in Stage B1 dogs, saving money and avoiding unnecessary drug administration.
3. Baseline for Monitoring: It establishes a baseline of chamber sizes, allowing the cardiologist to track the exact rate of progression over time.

The Case for Empiric Treatment (Murmur + X-ray)

The 2025 VetCompass study provides strong evidence that if an echocardiogram is financially or logistically impossible, it is clinically reasonable to start pimobendan based on a loud murmur and radiographic heart enlargement alone.

The authors of the study, supported by commentary from trial investigators (including Professor Adrian Boswood), noted that:

• The significant survival benefit and reduction in CHF risk were observed in a cohort where nearly half of the treated dogs did not have an echocardiogram.
• In small breed dogs (under 15 kg) over 6 years of age, a loud (Grade IV/VI or louder) left-apical systolic murmur has an extremely high predictive value for degenerative mitral valve disease. The likelihood of the murmur being caused by another cardiac pathology is very low.
• Thoracic radiographs (which are cheaper and can be performed in any primary-care practice) can document heart enlargement (VHS >= 11.5) and rule out active congestive heart failure.

Decision Protocol for Owners

If you are weighing the cost of diagnostics, consider this step-by-step decision framework:

1. Heart Murmur Detected
   • Grade I–II Murmur: Stage B1 is presumed. Monitor every 6–12 months. No medication is indicated at this time.
   • Grade III–VI Murmur: Check if an echocardiogram is affordable and available.
     • Echocardiogram Available: Perform echocardiography.
       • Criteria Met (LA/Ao >= 1.6 and LVIDd >= 1.7): Stage B2 is confirmed. Initiate pimobendan treatment under veterinary guidance.
       • Criteria Not Met: Stage B1 is confirmed. Monitor without medication.
     • Echocardiogram Unavailable/Unaffordable: Perform thoracic radiographs (chest X-rays).
       • Heart Enlargement Present (VHS >= 11.5) and Lungs Clear: Stage B2 is presumed. Initiate pimobendan treatment.
       • No Heart Enlargement (VHS < 11.5): Stage B1 is presumed. Monitor without medication.
       • Active Fluid in Lungs (Pulmonary Edema) Present: Stage C is confirmed. Initiate emergency congestive heart failure therapy.

This protocol ensures that dogs are not started on lifelong, expensive medication without evidence of cardiac enlargement, while still offering a path to treatment for owners who cannot afford referral to a cardiologist.

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Life expectancy: how fast MMVD progresses and a prognosis by stage

Prognosis in dogs with MMVD depends heavily on the stage at which the disease is detected and how quickly it progresses. The progression rate varies significantly between individual dogs.

1. Stage A and Stage B1

Dogs in Stage A and B1 have a normal life expectancy. Many dogs diagnosed with a Grade II murmur in Stage B1 live for several years without ever progressing to Stage B2 or showing clinical signs. The disease may remain static for the remainder of the dog's natural life, with death occurring from unrelated, non-cardiac causes.

2. Stage B2

Once a dog enters Stage B2, the heart has begun to enlarge, indicating that the compensatory mechanisms are starting to be strained. However, with appropriate intervention:

• The preclinical phase (Stage B2) is long. The EPIC trial showed that dogs starting pimobendan at B2 stayed free of heart failure for a median of 3.3 years (1,228 days).
• Overall survival from the time of Stage B2 diagnosis averages 3 to 4 years, depending on breed and individual response.

3. Stage C (Congestive Heart Failure)

When a dog develops pulmonary edema and enters Stage C, the prognosis becomes more guarded. However, modern veterinary cardiology has significantly improved survival times:

• With standard quadruple therapy (pimobendan, furosemide, ACE inhibitor, and spironolactone), the median survival time for dogs in Stage C MMVD is approximately 12 to 18 months.
• Some dogs with good compliance and slow-progressing disease can live comfortably in Stage C for 2 years or more.
• Once a dog has experienced heart failure, management shifts to maintaining quality of life, adjusting diuretic doses, and close home monitoring. For detailed guidance on managing this advanced stage, read our review of congestive heart failure in dogs.

The Breed Trajectory: Cavalier King Charles Spaniels

The Cavalier King Charles Spaniel (CKCS) is the classic poster child for MMVD.

• Unlike most other breeds where MMVD is a disease of geriatric dogs (onset at 10–12 years), Cavaliers can develop murmurs much earlier, often by 5 or 6 years of age.
• Roughly 50% of Cavaliers have a murmur by 5 years of age, and nearly 100% will have one if they live to 10 years.
• Because the disease starts earlier in this breed, the progression can be faster. However, the response to pimobendan in Stage B2 Cavaliers is highly effective, and the drug remains the cornerstone of extending their lifespan. Breeding guidelines recommend that Cavaliers should not be bred if they develop a murmur before 5 years of age, or if their parents developed a murmur before 5 years of age.

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Frequently Asked Questions

How long will a dog live with mitral valve disease?

The life expectancy varies by the stage of the disease. A dog in Stage B1 (murmur but no heart enlargement) can live a normal lifespan of several years without any heart issues. Once a dog progresses to Stage B2 (heart enlargement present), starting pimobendan gives them a median of 3 years before developing heart failure. If a dog reaches Stage C (active congestive heart failure), the median survival time with medication is typically 12 to 18 months, though some dogs can live comfortably for longer.

What is Stage B2, and why does pimobendan start there?

Stage B2 represents the preclinical phase of MMVD where the leak in the mitral valve has become severe enough to cause the heart chambers to enlarge (remodel), but the dog has not yet developed fluid in the lungs (congestive heart failure). Pimobendan is started at this stage because the landmark EPIC trial proved that starting it here delays the onset of heart failure by a median of 462 days (15 months) and extends overall survival. Starting it earlier (Stage B1) has shown no clinical benefit.

Can my dog take pimobendan if I can't afford an echocardiogram?

Yes. While an echocardiogram is the gold-standard diagnostic tool, the 2025 VetCompass study of 928 dogs proved that primary-care dogs derived a massive survival benefit and reduction in heart failure risk from pimobendan even when nearly half of them did not receive an echocardiogram. If an echo is financially out of reach, your veterinarian can perform chest X-rays to look for heart enlargement (VHS >= 11.5) and rule out fluid in the lungs. If enlargement is present, starting pimobendan is a highly reasonable, evidence-backed decision.

How fast does MMVD progress in a Cavalier King Charles Spaniel?

Cavalier King Charles Spaniels are genetically predisposed to MMVD, causing them to develop the disease much earlier in life (often by 5 or 6 years of age) and progress more rapidly than other small breeds. However, the disease still moves over a timeframe of years, not weeks. Early detection through annual vet exams, tracking the murmur grade, and screening with X-rays or echocardiography once a murmur is heard are key to starting medication at the exact moment the heart begins to enlarge.

When is mitral valve disease an emergency?

MMVD becomes a life-threatening emergency when the dog develops congestive heart failure (fluid in the lungs) or experiences a chordae tendineae rupture (sudden tearing of the valve support strings). Emergency signs include:

• A resting respiratory rate (sleeping breathing rate) that exceeds 40 breaths per minute.
• Labored, heavy, or open-mouth breathing.
• Constant coughing, particularly when resting or lying down.
• Coughing up pinkish, frothy fluid.
• Sudden collapse, severe weakness, or fainting spells.
• Pale, blue, or purple gums. If you observe any of these signs, seek immediate veterinary emergency care.

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Sources

1. ACVIM 2019 Consensus Guidelines: Keene, B. W., Atkins, C. E., Bonagura, J. D., Fox, P. R., Häggström, J., Luis Fuentes, V., Oyama, M. A., Rush, J. E., Stepien, R., & Uechi, M. (2019). ACVIM consensus guidelines for the diagnosis and treatment of myxomatous mitral valve disease in dogs. Journal of Veterinary Internal Medicine, 33(3), 1127–1140. https://pmc.ncbi.nlm.nih.gov/articles/PMC6524084/
2. The EPIC Trial: Boswood, A., Häggström, J., Gordon, S. G., Wess, G., Stepien, R. L., Oyama, M. A., Keene, B. W., Bonagura, J. D., MacDonald, K. A., Patteson, M., Smith, S., Wilshaw, J., Wegener, T., Schindler, E., Belfort, C. O., Duke-Novakovski, T., Shipley, H., Filion, R., Chetboul, V., & Watson, P. (2016). Effect of pimobendan in dogs with preclinical myxomatous mitral valve disease and cardiomegaly: The EPIC study—A randomized clinical trial. Journal of Veterinary Internal Medicine, 30(6), 1765–1779. https://pubmed.ncbi.nlm.nih.gov/27678080/
3. The 2025 VetCompass Study: Pegram, C., Diaz-Ordaz, K., Brodbelt, D. C., Chang, Y. M., Boswood, A., & Church, D. B. (2025). Emulating the EPIC trial using VetCompass primary-care data: Causal effects of pimobendan in UK dogs with grade IV/VI heart murmurs. PLOS ONE, 20(6), e0325695. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0325695
4. RVC VetCompass Summary: Royal Veterinary College. (2025). Big data from VetCompass reaffirms value of pimobendan in management of canine heart disease. RVC VetCompass News. https://www.rvc.ac.uk/vetcompass/news/big-data-from-vetcompass-reaffirms-value-of-pimobendan-in-management-of-canine-heart-disease
5. MMVD Prevalence Study: Mattin, M. J., Boswood, A., Church, D. B., López-Alvarez, J., McGreevy, P. D., O'Neill, D. G., Thomson, P. C., & Brodbelt, D. C. (2015). Prevalence of and risk factors for degenerative mitral valve disease in dogs attending primary-care veterinary practices in England. Journal of Veterinary Internal Medicine, 29(3), 847–854. https://pubmed.ncbi.nlm.nih.gov/25915692/
6. Cornell Reference: Cornell University College of Veterinary Medicine. (2023). "Leaky Valve Disease" of Older Dogs. Cornell Riney Canine Health Center. https://www.vet.cornell.edu/hospitals/services/cardiology/leaky-valve-disease-older-dogs
7. Cardiac Education Group: Cardiac Education Group. (2020). ACVIM MMVD Consensus Infographic & Staging Summary. https://cardiaceducationgroup.org/