Mitral valve disease in dogs: a complete guide

For most owners, the first hint is a passing comment at the end of an otherwise routine checkup. The vet lifts the stethoscope, pauses, and says something like, "I'm hearing a soft murmur on the left side — it's very mild, but I want to keep an eye on it." You nod, take the information in, and maybe look it up in the parking lot on your phone. That quiet moment is, for the majority of dogs who will develop heart disease, the beginning of a long story.

Myxomatous mitral valve disease — usually shortened to MMVD or MVD — is the single most common heart condition in dogs. By some estimates, more than three out of every four small-breed dogs over the age of ten have some degree of it. In Cavalier King Charles Spaniels the numbers are even more striking: roughly half are affected by age five, and nearly all are affected by age ten. It is the disease behind the vast majority of canine heart murmurs, the most common cause of congestive heart failure in dogs, and the reason medications like pimobendan have become household vocabulary for so many pet owners.

The disease sounds scary at first, and advanced MVD is indeed serious. But the story is not usually a fast one. Many dogs live for years between the first murmur and any meaningful change in quality of life. The goal of this guide is to give you a clear, unhurried picture of what the disease is, why it happens, what the different stages mean, how it is treated at each stage, and what you can do at home to help your dog live as well and as long as possible with it.

What mitral valve disease actually is

A healthy heart has four chambers and four one-way valves that keep blood flowing in a single direction. The mitral valve sits between the two chambers on the left side — the left atrium above and the left ventricle below. Every time the heart beats, the left ventricle contracts and pushes oxygen-rich blood out to the body through the aorta. The mitral valve snaps shut during that contraction to prevent blood from leaking backward into the atrium.

In mitral valve disease, the leaflets of this valve thicken, become nodular, and lose their crisp shape over time. The small cords that anchor the leaflets (the chordae tendineae) stretch and sometimes rupture. As the valve degenerates, it no longer closes completely. With each heartbeat, a portion of blood squirts backward into the left atrium instead of moving forward out to the body. This backward flow is what veterinarians call mitral regurgitation, and the turbulence it creates is the heart murmur your vet can hear through the stethoscope.

The heart responds by working harder and by remodeling. The left atrium enlarges to accommodate the extra volume of blood. The left ventricle thickens and dilates to pump more forcefully. For a long time, these changes keep things in balance, and the dog feels and acts entirely normal. But eventually — sometimes years later, sometimes sooner — the compensating mechanisms reach their limit. Pressure backs up into the lungs, fluid leaks into the lung tissue, and the dog develops congestive heart failure.

It is important to understand that MVD is a slow, chronic condition. Unlike a heart attack in humans, it does not typically arrive as a sudden catastrophic event. It progresses quietly through stages, and where your dog sits on that ladder — not just the diagnosis itself — is what shapes prognosis and treatment.

Why dogs get mitral valve disease

MVD is overwhelmingly a disease of small and medium-breed dogs, and the tendency is largely inherited. Certain breeds are dramatically overrepresented:

• Cavalier King Charles Spaniels — the classic example, with disease often developing as early as 4 to 6 years of age
• Chihuahuas
• Dachshunds
• Miniature and Toy Poodles
• Miniature Schnauzers
• Yorkshire Terriers
• Shih Tzus
• Maltese
• Bichon Frises
• Pomeranians
• Papillons
• Cocker Spaniels

Large breed dogs can develop MVD but do so far less often, and when they do, it is typically milder and later in life. In large breeds, dilated cardiomyopathy (DCM) is a more common cause of heart failure, and distinguishing the two matters because the treatments overlap but are not identical.

Beyond breed and genetics, age is the biggest risk factor. The valve degenerates gradually, and the number of affected dogs climbs steadily through the senior years. Dental disease may contribute modestly as well, because chronic oral bacteria can seed the bloodstream and irritate heart valves, which is one more reason to take senior dental care seriously.

The signs to watch for

For much of its course, MVD is a disease with no outward symptoms at all. The murmur is detectable long before the dog looks or acts sick — often by years. When signs do appear, they tend to creep in gradually, and many owners attribute them to normal aging until a more obvious episode prompts a closer look.

A soft cough, especially at night or after lying down

A dry, honking, or hacking cough is one of the most classic signs. It often worsens in the evening, shortly after lying down, or first thing in the morning. The cause is usually a combination of the enlarged left atrium pressing on the airways and, in more advanced disease, fluid in or around the lungs. Not every coughing senior dog has heart disease — tracheal collapse, chronic bronchitis, and laryngeal paralysis all cause cough too — but in a small-breed senior, a new cough is a meaningful reason to listen to the chest.

Reduced exercise tolerance

Your dog who used to want a full walk may start asking to turn back earlier. The dog who happily chased a ball across the yard may slow down after one or two throws. Because the change is gradual and lines up with how we already picture "slowing down with age," it is easy to miss. Compare her to a year ago, not yesterday.

Increased resting respiratory rate

The single most useful thing you can do at home for a dog with MVD is count her sleeping breaths. A healthy dog at rest takes fewer than 30 breaths per minute. A consistently elevated sleeping respiratory rate — especially one that trends upward over several days — is one of the earliest and most reliable signs that fluid is starting to accumulate. Counting takes thirty seconds: watch the chest rise and fall, count, and double the number. Many cardiologists now recommend that owners log this every few days once their dog is in Stage B2 or C disease.

Labored or fast breathing at rest

Rapid breathing, visible effort in the chest and belly, flared nostrils, or extended neck are all signs of respiratory distress. A dog who stands or sits with her elbows splayed and refuses to lie down may be struggling to breathe. This is a same-day veterinary problem, not a wait-and-see one.

Fainting or collapse

Brief episodes of weakness or collapse, especially during excitement, exercise, or coughing, can occur in MVD. They are caused either by the heart briefly failing to deliver enough blood to the brain or by a cough-induced drop in blood pressure. Any episode of collapse in a dog with a known murmur warrants prompt cardiac evaluation.

A bluish or gray tongue and gums

Normally pink gums turning gray, blue, or very pale — particularly during exertion or a coughing fit — signal that tissues are not getting enough oxygen. This is an emergency.

Abdominal swelling

In dogs with right-sided heart involvement, fluid can accumulate in the belly, making it look swollen or pot-bellied. This is less common than the left-sided picture (fluid in the lungs) but is an important sign when it appears.

How MVD is diagnosed

Because the disease is so often silent in its early stages, diagnosis usually begins with something your vet hears during a routine exam and progresses through imaging once concern is raised.

Physical examination and murmur grading

Murmurs are graded from I to VI. A grade I murmur is barely audible and requires a quiet room and careful listening. A grade VI is so loud it can be felt with a hand on the chest wall. Higher grade does not automatically mean worse disease, but in MVD the grade does tend to correlate with severity, and a murmur that has clearly gotten louder over time is a prompt to investigate further.

Chest X-rays (radiographs)

X-rays show the size and shape of the heart and, critically, the condition of the lungs. They are the best test for determining whether fluid has started to accumulate in the lungs (pulmonary edema, the defining feature of congestive heart failure). They also provide an objective measurement called the vertebral heart score (VHS) that tracks heart enlargement over time. X-rays are often the first imaging step after a murmur is discovered.

Echocardiogram (cardiac ultrasound)

Echocardiography is the gold standard for staging MVD and the test that determines when treatment should start. A trained veterinary cardiologist (or experienced general practitioner with cardiac ultrasound training) can visualize the mitral valve directly, measure the thickness and enlargement of the left atrium and left ventricle, quantify how much blood is leaking backward, and look for any complicating features such as pulmonary hypertension or ruptured chordae. The echo is non-invasive, usually well tolerated without sedation, and the findings drive every subsequent treatment decision.

NT-proBNP blood test

NT-proBNP is a biomarker released when the heart muscle is stretched. A blood test can help screen for significant heart disease, distinguish cardiac from respiratory causes of cough or breathing difficulty, and identify which dogs with murmurs most urgently need an echocardiogram.

Blood pressure and routine bloodwork

A full cardiac workup includes a blood pressure measurement, chemistry panel, and urinalysis. Kidney function matters because several heart medications are processed or affect the kidneys. High blood pressure, if present, needs its own treatment and can worsen heart disease if ignored.

Electrocardiogram (ECG)

An ECG records the electrical activity of the heart and is essential when arrhythmias are suspected. Most dogs with MVD have a normal rhythm, but advanced disease can produce atrial fibrillation or other arrhythmias that change management.

Staging: the ACVIM classification

Veterinary cardiologists use a staging system developed by the American College of Veterinary Internal Medicine (ACVIM) to describe where a dog sits in the course of the disease. Staging matters enormously because it determines whether medication is indicated and which medications are appropriate.

Stage A: A dog at high risk of developing MVD because of breed (for example, a young Cavalier King Charles Spaniel) but with no murmur and no structural heart changes. No medication; routine monitoring with an annual exam.

Stage B1: A murmur is present and the valve is leaking, but echocardiographic measurements show the heart has not significantly enlarged. No medication is recommended at this stage. The dog feels normal and behaves normally. Rechecks every 6 to 12 months are typical.

Stage B2: The valve is leaking enough that the left atrium and/or left ventricle have enlarged, but the dog still has no outward symptoms. This is the stage at which pimobendan is recommended. The landmark EPIC study showed that starting pimobendan in Stage B2 delays the onset of congestive heart failure by approximately 15 months. Identifying dogs in this stage is arguably the single most important reason to get an echocardiogram when a murmur is discovered.

Stage C: Current or past signs of congestive heart failure are present. Multi-drug therapy is required. Most dogs in this stage are hospitalized briefly at the time of their first CHF episode for stabilization and then transition to a lifelong oral medication regimen at home.

Stage D: Advanced or refractory heart failure that no longer responds well to standard therapy. Specialist management, higher doses, additional medications, and careful quality-of-life conversations become central.

Treatment at each stage

Unlike many chronic diseases, MVD treatment follows a clear stage-based roadmap. Starting medication too early has not been shown to help and may cause harm. Starting at the right time can add many good months or years to a dog's life.

Pimobendan (Vetmedin)

Pimobendan is the single most impactful medication in MVD. It helps the heart contract more efficiently and also relaxes the blood vessels it pumps against, which reduces the workload on the struggling heart. The EPIC trial in 2016 established that pimobendan given in preclinical Stage B2 disease significantly delays the onset of heart failure. Once heart failure develops (Stage C), pimobendan remains a cornerstone of therapy and is generally continued for life.

Furosemide (Lasix)

Furosemide is a loop diuretic that pulls excess fluid out of the body and is the frontline treatment for pulmonary edema. It is started when congestive heart failure develops and is continued long-term in most Stage C dogs. Dogs on furosemide drink more water, urinate more, and need their kidney values and electrolytes monitored periodically. A variant, torsemide, is more potent and is often used when furosemide loses effectiveness in advanced disease.

ACE inhibitors (enalapril, benazepril)

ACE inhibitors block a hormonal pathway that drives blood pressure and fluid retention. They are commonly added in Stage C and are sometimes used in Stage B2. They need modest kidney monitoring and should be dose-adjusted if the kidneys are already compromised.

Spironolactone

Spironolactone is a mild potassium-sparing diuretic that also blocks the hormone aldosterone, which drives long-term cardiac remodeling. It is frequently part of multi-drug protocols in Stage C disease.

Sildenafil

Some dogs with advanced MVD develop pulmonary hypertension — high pressure in the blood vessels of the lungs — which can cause cough, exercise intolerance, and fainting. Sildenafil (yes, the same molecule as Viagra) lowers this pressure and can substantially improve comfort and activity in dogs who need it.

Antiarrhythmic medications

Dogs who develop atrial fibrillation or other rhythm problems may need medications such as diltiazem or digoxin to control the rate. These are chosen selectively based on ECG findings and overall status.

Surgery: mitral valve repair

Open-heart surgical repair of the mitral valve is now performed at a small number of specialist centers around the world and can, in successfully selected and treated dogs, effectively cure the disease. It is expensive, requires travel to a specialized center, and is not appropriate for every dog. For owners of dogs in Stage B2 or early Stage C with good overall health, surgery is increasingly a conversation worth having with a board-certified veterinary cardiologist.

Dietary sodium and caloric adjustment

Moderate sodium restriction is generally recommended once a dog is in Stage C. Prescription cardiac diets exist, but the most important practical step is usually to stop feeding salty table scraps, deli meats, cheese, and processed treats. Maintaining a lean body condition also reduces cardiac workload; paradoxically, though, dogs with advanced heart disease can develop cardiac cachexia — muscle loss despite adequate food — and may need more protein and calories, not fewer, to hold their weight.

Monitoring at home

The quality of home monitoring often determines how well a dog with MVD does. Two simple practices give you outsized power to catch problems early.

Sleeping respiratory rate. Once your dog is in Stage B2 or C, count her breaths while she is fully asleep — not panting, not in a hot room, not dreaming. Watch the chest rise and fall for 30 seconds and double the number. Under 30 is normal. A sustained rate above 40, or a clear upward trend over several days, often signals fluid starting to back up before anything looks obviously wrong. Many owners keep a simple log in the notes app on their phone, and the trend matters more than any single reading. Dogs who are caught on an upward trend and seen promptly often get a quick furosemide adjustment and avoid an overnight emergency visit.

Daily weight and appetite check. Sudden weight gain (sometimes two or three pounds over a few days) can represent fluid retention, and weight loss in a previously stable dog can signal decompensation or cardiac cachexia. Note anything that looks like a change, and don't dismiss a skipped meal in a dog with advanced heart disease.

Making your home MVD-friendly

Keep a calm, predictable routine

Excitement drives up heart rate and blood pressure. Dogs with advanced MVD can cope with normal daily life but tolerate chaos, extended travel, and exuberant visitors less well. Predictable meal times, medication times, and rest periods all help.

Adjust exercise without eliminating it

Most dogs with MVD benefit from continued gentle exercise — short, calm walks adjusted to what your dog tolerates comfortably. What to avoid is intense bursts of activity, long hikes beyond her fitness, and play that pushes her to the edge of breathlessness. Watch her effort and the distance she wants to go; she will tell you.

Control temperature

Heat is hard on any struggling heart. Keep the home cool in summer, avoid walks in midday heat, and never leave a dog with heart disease in a warm car even briefly. In winter, keep her warm and dry; cold, wet walks can tax her too.

Elevated resting spots and soft bedding

Some dogs with early heart failure prefer to rest with the chest slightly elevated, which eases breathing. A firm bolster bed or a favorite couch cushion often suits them well. Keep at least one comfortable resting spot per floor of the house so she does not have to climb stairs to lie down.

Take dental health seriously

Chronic oral infection can seed bacteria into the bloodstream, and in advanced heart disease this can worsen valve damage. Daily brushing, vet-approved dental chews, and — when safe — professional cleanings all protect the heart as well as the mouth. Anesthesia for dentistry in a dog with MVD is more complex than in a healthy dog but is often still reasonable when carefully planned with your veterinary team.

Build a medication routine you can sustain

Dogs in Stage C often take three to five different medications on a strict schedule. Pill organizers, phone alarms, and pill pockets all help. Missing doses of furosemide or pimobendan can trigger a heart failure episode, so consistency genuinely matters.

What to avoid

• Skipping the echocardiogram when a murmur is first identified. Dogs in Stage B2 benefit enormously from starting pimobendan at the right time, and that window can only be identified with an echo. Waiting until heart failure develops is a missed opportunity.
• Starting medications based on breed alone. Pimobendan was specifically not shown to help Stage B1 dogs in rigorous trials, and starting too early offers no benefit. Staging first, medicating second, is the right order.
• Salty table scraps and processed treats. Deli meat, bacon, cheese, pretzels, and most commercial jerky treats are very high in sodium and can worsen fluid retention in a dog with heart failure.
• Stopping medications when she "seems fine." Dogs in Stage C feel good precisely because the medications are working. Stopping them often leads to relapse within days.
• Over-the-counter human cough medicines. These can mask worsening heart failure, contain ingredients toxic to dogs, or interfere with cardiac medications. Never give human cough suppressants without veterinary guidance.
• Ignoring an upward sleeping respiratory rate trend. Owners who catch this early and call the vet often get a small medication adjustment and avoid an overnight emergency. Owners who wait for obvious distress sometimes do not.
• High-sodium IV fluids without cardiac assessment. Dogs with heart disease can decompensate dangerously on the volume of fluids that would be safe for a healthy dog. Always remind any vet treating your dog — even for unrelated problems — that she has heart disease.

When to see the vet

Dogs with diagnosed MVD typically need rechecks every 6 to 12 months in Stage B1, every 3 to 6 months in Stage B2, and every 1 to 3 months in Stage C, though the exact cadence depends on the individual dog and how recently she was stabilized. Between visits, several changes warrant earlier attention.

Call your vet soon if your dog shows:

• A sleeping respiratory rate consistently above 40 breaths per minute, or a clear upward trend over several days
• A new or worsening cough, especially at night or after lying down
• Reduced appetite or noticeable weight loss
• Reluctance to walk or play as far as usual
• A sudden weight gain that could reflect fluid retention
• Episodes of weakness or near-collapse

Seek emergency care immediately if your dog shows:

• Labored or noisy breathing at rest, or breathing with the belly as well as the chest
• Blue, gray, or very pale gums or tongue
• Inability or refusal to lie down because breathing is too difficult when flat
• A collapse that does not resolve quickly
• Continuous coughing, especially with pink or foamy fluid
• Severe lethargy with rapid breathing

Acute congestive heart failure is one of the few cardiac crises where minutes genuinely matter. Dogs who arrive at the emergency room early almost always do better than dogs whose owners wait and hope overnight.

Prognosis: what to expect

Prognosis for MVD varies enormously by stage at diagnosis and how quickly the disease progresses, and it is one of the things owners most want to ask and most struggle to get a straight answer about. A few honest generalities help.

Dogs in Stage B1 often live many years without ever progressing to heart failure, and many ultimately die of something entirely unrelated to the heart. Dogs in Stage B2 who start pimobendan at the right time see the onset of congestive heart failure delayed by roughly 15 months on average compared to similar dogs who do not receive it. Once dogs reach Stage C, median survival with modern multi-drug therapy is typically around 12 to 18 months, though some dogs — particularly those caught early and managed carefully — live considerably longer. Dogs in Stage D tend to have shorter prognoses, measured in weeks to a few months, though specialist care and intensified therapy can extend that meaningfully in some cases.

These are averages across many dogs, not predictions for any individual dog. Breed, overall health, kidney function, how well medications are tolerated, whether arrhythmias or pulmonary hypertension develop, and the strength of monitoring at home all shape what her actual experience will be.

Living well with a dog who has mitral valve disease

A diagnosis of mitral valve disease is weighty news, especially for owners of young Cavaliers or other breeds where the disease often arrives earlier than anyone expects. But the long arc of MVD is genuinely different from many other serious diagnoses. There is real, evidence-based medicine behind the treatment decisions. The disease is usually slow. The tools to monitor it at home are simple and effective. And many dogs live years of comfortable, ordinary, joyful life between the first murmur and the last goodbye.

Get the echocardiogram. Know her stage. Start pimobendan if and when it is indicated. Watch her sleeping breathing rate. Keep her calm, keep her cool, keep her dental health solid, and keep her in a consistent medication routine if she reaches Stage C. Call early, not late, when something changes.

The murmur your vet hears today is a piece of information, not a verdict. It is a starting place — an invitation to pay closer attention, to set up the right monitoring, and to be ready with the right tools if and when the disease progresses. For most dogs, what follows is not a short story. It is a long one, with a great many good pages still ahead.

This article provides general educational information about mitral valve disease in dogs. It is not a substitute for individualized veterinary advice. Every dog is different, and diagnosis, staging, and treatment decisions should always be guided by a veterinarian — and ideally, for Stage B2 or more advanced disease, a board-certified veterinary cardiologist — who can examine your dog and interpret her specific imaging, bloodwork, and history. Never start, stop, or change the dose of cardiac medications without veterinary guidance, and never give your dog human cough medicines, sodium-rich foods, or over-the-counter supplements marketed for heart health without explicit instruction. If your dog develops labored breathing at rest, blue or gray gums, sustained collapse, or continuous coughing with pink or foamy fluid, seek emergency veterinary care immediately rather than waiting for a scheduled appointment.