Mitral Valve Disease

Written by Dr Kelly Yeo, Veterinarian Last updated: October 2026

Mitral valve disease is one of the most common heart conditions affecting older dogs, particularly small and medium-sized breeds. It is often first suspected when a veterinarian hears a heart murmur during a routine examination.

Hearing that your dog has a heart murmur can be worrying, especially when they still seem perfectly well at home. However, a murmur does not necessarily mean that your dog is in heart failure or needs medication immediately.

Some dogs remain stable for years without treatment, while others gradually develop enlargement of the heart and eventually need medication. The most useful next step is to establish what is causing the murmur and, if mitral valve disease is confirmed, determine its stage. This helps us decide what to monitor, when treatment may help and what the diagnosis could mean for your dog's future.

Important disclaimer: This information is for educational purposes only and is not a substitute for professional veterinary advice. Always work closely with your veterinarian for personalised diagnosis, treatment, and monitoring.

Mitral valve disease, also called myxomatous mitral valve disease (MMVD) or degenerative mitral valve disease, develops when the valve between the heart's left atrium and left ventricle gradually changes shape and no longer closes tightly.

Each time the heart pumps, some blood leaks backwards through the valve. This is called mitral regurgitation.

In the early stages, the heart can often cope with the leakage, and a dog may have no symptoms at all. Over time, the left side of the heart may enlarge as it handles the extra blood volume. In some dogs, the condition eventually progresses to congestive heart failure, when fluid accumulates in the lungs and makes breathing difficult.

The rate of progression varies widely. A dog with a mild leak may remain well for years, while another dog may need closer monitoring or treatment much sooner.

Age and genetics both contribute. Small breeds are particularly susceptible, including Cavalier King Charles Spaniels, Maltese, Chihuahuas, Miniature and Toy Poodles, Yorkshire Terriers, Shih Tzus and Pomeranians.

Cavalier King Charles Spaniels can develop the condition at a younger age than many other breeds, so regular heart examinations are particularly worthwhile.

Mitral valve disease is generally not caused by anything an owner has done wrong. If it has been diagnosed, I would concentrate on finding out how advanced it is and making an appropriate plan for monitoring or treatment.

A murmur is an extra sound that your veterinarian hears through a stethoscope. With mitral valve disease, it is usually caused by blood leaking backwards across the valve.

Murmurs are graded from one to six according to how loud they sound. Although a louder murmur may increase concern about more significant disease, the grade alone cannot tell us how much the heart has enlarged or whether medication is needed. Not every heart murmur is caused by mitral valve disease, either.

An echocardiogram, or ultrasound of the heart, is usually the most informative test for identifying the valve problem and assessing the heart's structure and function. Your veterinarian may also recommend chest X-rays, particularly if there are breathing changes or a need to assess heart size and the lungs.

Many dogs in the early stages have no noticeable symptoms. A murmur may be the only clue during a routine check-up.

As the disease becomes more advanced, possible changes include reduced stamina, taking longer to recover after walks, sleeping less comfortably, faster breathing when resting, restlessness at night, reduced appetite and gradual weight or muscle loss. Some dogs may faint or become unusually weak.

Coughing can also occur, but I would be careful about assuming that a cough is coming from the heart. Small, older dogs can have tracheal collapse, chronic bronchitis and other airway conditions alongside a heart murmur. A dog with a murmur and a cough needs an assessment to establish the cause, rather than automatically being diagnosed with congestive heart failure.

I would be more concerned about a change in breathing than an isolated cough. If your dog starts breathing rapidly while resting, cannot settle comfortably or is unusually weak, seek veterinary assessment promptly. Marked breathing difficulty, blue or grey gums, fainting or collapse require immediate attention.

Veterinary cardiologists commonly use the American College of Veterinary Internal Medicine (ACVIM) staging system. The stage matters because different dogs need very different treatment plans.

A dog with a heart murmur does not automatically have Stage B2 disease. The decision to begin pimobendan depends on specific findings, including the degree of cardiac enlargement on echocardiography and, in many cases, chest X-rays. This is why I would not make treatment decisions from the sound of the murmur alone.

The answer depends very much on the stage of disease and on the individual dog.

Dogs in Stage B1 may remain stable for a long time without medication. When the heart has enlarged enough to meet Stage B2 criteria, starting pimobendan can delay the development of congestive heart failure in suitable dogs.

For dogs that have progressed to Stage C, the outlook becomes more guarded, although many still respond well to treatment and enjoy meaningful, comfortable time at home. Dogs with Stage D disease usually need more intensive management because symptoms have become difficult to control.

When discussing prognosis, I would consider the heart's size and function, breathing rate, kidney health, response to treatment, appetite, body weight and muscle condition. I would also ask about the things the dog still enjoys doing. Two dogs at the same stage can have quite different experiences and outcomes.

There is no single life-expectancy figure that applies to every dog with mitral valve disease. If your dog has just been diagnosed, ask your veterinarian which stage they are in and what findings are most relevant to their prognosis.

A heart murmur often prompts the initial investigation. The most useful test for confirming degenerative mitral valve disease and assessing its effects is an echocardiogram.

Depending on your dog's symptoms and examination, your veterinarian may recommend chest X-rays to assess heart size and look for pulmonary oedema, blood pressure measurement, blood tests to assess kidney function and electrolytes, or an ECG if an abnormal heart rhythm is suspected. NT-proBNP testing can help in selected situations but does not replace a complete cardiac assessment.

Follow-up intervals depend on the stage and on how quickly the disease appears to be progressing. A dog with stable early disease may need periodic rechecks, while one with heart failure generally needs much closer review and monitoring of medication effects.

I would also consider other conditions common in older dogs. Kidney disease, pulmonary hypertension, respiratory problems and changes in muscle condition can all affect how we manage a patient with mitral valve disease.

Stage B1: Dogs are generally monitored without starting cardiac medication. Your veterinarian will advise when to repeat an examination or heart scan, especially if the murmur changes or new symptoms appear.

Stage B2: Pimobendan is recommended for many dogs who meet the established criteria for significant heart enlargement. In the EPIC clinical trial, it delayed the combined outcome of congestive heart failure, cardiac-related death or euthanasia compared with placebo. The findings apply to dogs similar to those enrolled in the study; they should not be taken to mean that every dog with a murmur or a slightly enlarged heart needs the drug.

Stages C and D: Once congestive heart failure has occurred, treatment usually involves a combination of medications. These commonly include pimobendan and a diuretic such as furosemide to reduce fluid accumulation. Other medicines, including an ACE inhibitor or spironolactone, may be recommended depending on the patient's condition and the treating veterinarian's plan. Dogs with advanced or difficult-to-control failure may need specialist input and adjustments to their treatment.

Diuretics can affect hydration, kidney values and electrolytes. Dogs taking them generally need blood-test monitoring, and owners should not restrict drinking water unless their veterinarian has given a specific medical instruction. Never change or stop cardiac medication without discussing it with your vet.

Medication helps control the consequences of mitral valve disease, but it does not repair the damaged valve. Specialist surgical repair is possible in selected dogs, although it requires highly specialised facilities and expertise.

Another approach is transcatheter edge-to-edge repair, or TEER. This uses a device to bring parts of the leaking valve together and reduce regurgitation. It is available only in selected specialist centres, and not every dog is a suitable candidate.

A study published online in December 2025 followed 111 dogs undergoing TEER at one referral centre and reported encouraging intermediate outcomes. However, the procedure has risks, including serious complications, and the study did not compare TEER directly with medical treatment. It is best discussed with a veterinary cardiologist rather than viewed as a routine alternative to medication.

For dogs with known mitral valve disease, counting the sleeping respiratory rate can be a useful way to notice changes early.

Wait until your dog is asleep or deeply relaxed, not panting after exercise or because of the heat. Count each rise and fall of the chest as one breath. You can count for 30 seconds and double the result, or count for a full minute. Record the number so you can recognise your dog's usual pattern over time.

Many stable dogs have a sleeping respiratory rate below 30 breaths per minute. A persistent increase above their usual rate, repeated readings around or above 30 while asleep, or any new change in breathing effort should prompt a discussion with your veterinarian. Your dog's individual baseline matters, and one number cannot replace an assessment of their comfort and breathing.

If your dog is struggling to breathe, has blue or grey gums, collapses, or cannot settle because of breathing difficulty, seek emergency veterinary care rather than waiting to take more measurements.

Everyday care should be guided by the stage of disease and how your dog feels.

I generally encourage comfortable, regular activity for dogs with early disease. They do not automatically need to stop walking simply because they have a murmur. However, I would avoid forcing strenuous exercise, especially in hot or humid weather, and I would adapt walks if the dog tires easily or takes longer to recover. Dogs with congestive heart failure may be better suited to shorter, gentler outings.

Nutrition is also important. Maintaining a healthy weight and protecting muscle mass help support comfort and general health. Dogs with heart failure may benefit from moderating dietary sodium, but very strict restriction is not necessary for every dog with early disease and can be counterproductive if it reduces appetite. Your veterinarian can advise what is appropriate for your dog's stage and other medical conditions.

Some owners choose to give supplements such as CoQ10 or other products marketed for heart health. These can be considered alongside conventional treatment, but so far they have not reliably been shown to improve outcomes or slow the progression of mitral valve disease. They should never replace prescribed cardiac medication or recommended monitoring. Omega-3 fatty acids may be useful in selected dogs, particularly when appetite or body condition is a concern, but I would still recommend discussing any supplements with your veterinarian.

At home, I would keep track of breathing rate, coughing, appetite, activity, body weight and any changes in sleeping comfort. Taking medication as prescribed and attending recommended follow-ups are also important, particularly once a dog has developed heart failure.

If your dog has a new cough, a noticeable reduction in stamina, persistent loss of appetite, unexplained weight loss or a rising sleeping respiratory rate, arrange a veterinary assessment rather than assuming these changes are part of normal ageing.

Seek emergency care if your dog is struggling to breathe, has blue or grey gums, collapses, or is unable to settle because of severe breathing difficulty. Do not try to manage a breathing emergency by changing diuretic doses at home without veterinary advice.

Medication cannot reverse the degeneration of the mitral valve. It can, however, delay the onset of heart failure in selected dogs and help control symptoms once heart failure develops. Specialist procedures may be suitable for a small number of patients.

No. Some dogs have early disease and need monitoring only. The cause of the murmur, degree of heart enlargement and other test findings help determine whether medication is appropriate.

Not necessarily. Coughing can be caused by airway and lung conditions as well as heart disease. Dogs can also have more than one condition at the same time. Your veterinarian may recommend chest X-rays or other testing to work out what is causing it. You can also read our article on why dogs cough.

Yes, particularly in predisposed breeds such as Cavalier King Charles Spaniels. A murmur detected in a younger dog deserves an individual assessment because other heart conditions may also cause murmurs.

Usually not if your dog has early, stable disease and feels well. Exercise should be comfortable and appropriate to their condition. If your dog has heart failure, reduced stamina or breathing difficulties, ask your veterinarian for an individual activity plan.

For many dogs, a diagnosis of mitral valve disease is the beginning of a period of monitoring rather than an immediate change in daily life. I encourage owners to understand their dog's stage, keep track of changes at home and attend the recommended rechecks.

If heart failure develops, treatment becomes more involved. Our priorities then include keeping breathing comfortable, maintaining appetite and muscle condition, and preserving the activities the dog can still enjoy. A good management plan should change as the dog's needs change.

Dr Kelly Yeo, BVSc, graduated from the University of Melbourne in 2009. She is a small-animal veterinarian based in Singapore with a clinical interest in senior care, chronic disease, palliative care and canine longevity.