Mitral Valve Disease

Understanding heart murmurs, valve disease, monitoring, and long-term care

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

Mitral valve disease is the most common form of heart disease seen in dogs. It is especially common in small and medium-sized breeds as they enter middle age and their senior years.

If your dog has recently been diagnosed with mitral valve disease, or if your veterinarian has mentioned a heart murmur during a routine check-up, this guide will help you understand what the diagnosis means, what to monitor, and when treatment may be needed.

Heart disease can become serious in its advanced stages, and dogs with end-stage heart failure may unfortunately pass away from the condition. However, in the early stages of mitral valve disease, most dogs remain completely unaffected. With early detection and regular monitoring, many dogs can continue living normal, happy lives for a long time.

Mitral valve disease usually cannot be cured with medication, but it can often be managed very well when it is detected early, staged properly, and monitored consistently.

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 known as myxomatous mitral valve disease or MMVD, happens when the mitral valve in the heart gradually degenerates and begins to leak.

The mitral valve sits between the left atrium and the left ventricle. When the valve becomes thickened or weakened, it no longer seals properly. Blood then leaks backward into the left atrium each time the heart pumps.

This backward leakage is called mitral regurgitation.

At first, the heart can often compensate. The chambers may slowly enlarge to handle the extra blood volume, and many dogs still look completely normal at home.

Over time, if the valve leak becomes more significant, the heart may struggle to keep up. In some dogs, this can eventually lead to congestive heart failure, where fluid builds up in or around the lungs.

The condition is progressive, but the speed varies greatly. Some dogs remain stable for years. Others need treatment sooner. This is why regular monitoring matters.

Mitral valve disease is mainly age-related, but genetics play an important role.

It is most common in small and medium-sized breeds, including:

Cavalier King Charles Spaniels can develop mitral valve disease earlier than many other breeds. Regular heart screening is especially useful for this breed and other predisposed dogs.

Mitral valve disease is not usually caused by poor care. The more useful question is: what stage is the disease now, and what should be done next?

A heart murmur is an abnormal sound heard through the stethoscope. In dogs with mitral valve disease, it is usually caused by turbulent blood flow as blood leaks backward through the mitral valve.

Heart murmurs are commonly graded from Grade 1 to Grade 6, with Grade 1 being very soft and Grade 6 being very loud.

A low-grade murmur does not automatically mean your dog is in danger. Many dogs with low-grade murmurs live normal lives for years. However, murmur grade alone does not tell the full story. Further assessment is often recommended when a murmur is new, increasing, or found in a breed prone to mitral valve disease.

In the early stages, many dogs show no obvious symptoms. The only finding may be a heart murmur heard during a routine veterinary examination.

As the disease progresses, owners may notice:

These signs can be mistaken for normal ageing. In a dog with a known heart murmur, changes in breathing, coughing, stamina, appetite, or energy should be checked promptly.

Congestive heart failure can develop when the heart can no longer manage the leaking valve effectively and fluid begins to build up.

Signs may include:

One of the most useful things owners can monitor at home is resting respiratory rate. Count your dog's breaths when they are asleep or deeply resting. One rise and fall of the chest equals one breath. For many dogs, a sleeping or resting respiratory rate under 30 breaths per minute is reassuring, but the trend is just as important as the number.

Seek urgent veterinary attention if your dog has laboured breathing, blue or grey gums, collapse, severe weakness, or cannot settle because of breathing difficulty.

Mitral valve disease is often first suspected when a veterinarian hears a heart murmur during a physical examination.

Further evaluation may include:

An echocardiogram is the most useful test for confirming mitral valve disease and assessing valve leakage, heart chamber size, heart function, and complications such as pulmonary hypertension.

Treatment decisions should not be based on the murmur alone. They should be based on stage, heart size, symptoms, and concurrent problems.

Heart disease is commonly staged using the ACVIM system, from Stage A to Stage D.

A dog in Stage B1 may need monitoring only. A dog in Stage B2 may benefit from medication before symptoms appear. A dog in Stage C or D usually needs more active treatment and closer follow-up.

Dogs with mitral valve disease, especially those in heart failure, should be checked for concurrent issues such as high blood pressure, pulmonary hypertension, kidney disease, abnormal heart rhythms, and other senior-dog health conditions.

Kidney status is especially important because many medications used to manage heart failure are diuretics. Diuretics help remove excess fluid, but they can also place additional workload on the kidneys.

Patients with both heart and kidney disease must be managed carefully. The goal is to reduce fluid build-up without dehydrating the dog or worsening kidney function.

Treatment depends on the stage of disease. The goals are to reduce cardiac workload, manage fluid accumulation, delay progression where possible, and maintain quality of life.

Dogs in Stage B1 are usually monitored rather than medicated. Regular rechecks help detect progression before symptoms develop.

Dogs in Stage B2 have heart enlargement but no obvious symptoms. Pimobendan is commonly recommended for many dogs in this stage if they meet specific criteria. In suitable patients, this medication can help delay the onset of congestive heart failure.

This is one reason early diagnosis is valuable.

Dogs in congestive heart failure usually need a combination of medications. These may include:

Medication plans must be individualised. Dogs on diuretics need monitoring of kidney values and electrolytes because heart and kidney health are closely linked.

For dogs with more advanced mitral valve disease, a newer option called TEER may be available in some specialist centres.

TEER stands for transcatheter edge-to-edge repair. It is a minimally invasive procedure designed to improve mitral valve function by reducing the amount of leakage.

This procedure is still emerging in veterinary medicine and is not suitable for every patient. For most dogs, standard medical management remains the main approach.

Diet does not cure mitral valve disease, but it can support the overall treatment plan.

Important nutritional goals include maintaining a healthy body weight, avoiding obesity, preventing excessive muscle loss, supporting appetite, and avoiding very salty foods, especially in dogs with heart failure.

Dogs with congestive heart failure may benefit from moderate sodium restriction, although severe restriction is not always appropriate if appetite is poor. Avoid salty foods such as ham, bacon, sausages, cheese, salted broths, chips, and heavily seasoned leftovers.

Some supplements may be discussed with your veterinarian, including omega-3 fatty acids, CoQ10, taurine, and L-carnitine in selected cases.

Supplements should complement, not replace, prescribed heart medication.

Helpful home care steps include:

Dogs with early mitral valve disease can often continue normal gentle activity. Many benefit from regular low-to-moderate exercise as long as they are not pushed beyond what they can tolerate.

Avoid exercising in hot weather, long intense runs, rough play that causes breathlessness, and forcing walks when your dog wants to stop.

For dogs in heart failure, the aim is comfortable movement rather than fitness training. Shorter, slower walks may be better than long outings.

Dogs diagnosed in the early stages often enjoy many good years ahead. Dogs in Stage C can still have meaningful, comfortable time with appropriate treatment, but they need closer monitoring.

Prognosis depends on factors such as breed, age at diagnosis, murmur grade, heart size, ACVIM stage, resting respiratory rate, kidney function, blood pressure, pulmonary hypertension, response to medication, appetite, weight, and muscle condition.

In advanced disease, care may become more palliative. This means focusing on breathing comfort, appetite, sleep, calmness, and dignity.

The most important question is not only "How long does my dog have?" but also "How well is my dog living?"

Mitral valve disease cannot always be prevented, especially when genetics are involved, but early detection can improve outcomes.

Helpful steps include:

For senior dogs, heart checks are an important part of preventive care.

It varies significantly. Many dogs live for years after diagnosis with good management. Dogs in Stage B1 may remain stable for a long time. Dogs in Stage B2 may benefit from medication to delay heart failure. Dogs in Stage C or D need closer management because congestive heart failure has already developed.

Mitral valve disease is usually not curable with medication. Medication helps reduce workload on the heart, manage fluid build-up, delay progression in selected stages, and improve quality of life.

Specialist procedures such as TEER or surgical repair may be options for selected dogs.

No. Some dogs with murmurs have early disease and do not need medication yet. The decision depends on the cause of the murmur, heart size, echocardiogram findings, symptoms, blood pressure, and overall health.

No. Dogs can cough because of airway disease, tracheal collapse, bronchitis, infection, allergies, lung disease, or heart disease. In small-breed dogs, coughing may have more than one cause. A dog with a murmur and cough should be assessed carefully rather than assuming the cough is definitely from the heart.

Avoid salty foods, especially if your dog has heart failure or is on heart medication. Common foods to avoid include ham, bacon, sausages, cheese, salted broths, processed meats, chips, and heavily seasoned leftovers.

Omega-3 fatty acids are sometimes recommended for their anti-inflammatory benefits. Other commonly discussed supplements include CoQ10, taurine, and L-carnitine. Always discuss supplements with your veterinarian before use.

It is uncommon in young dogs, but it can happen, especially in predisposed breeds such as Cavalier King Charles Spaniels. Young dogs with murmurs should be assessed carefully.

The key is to understand the stage of disease, monitor breathing at home, attend regular veterinary rechecks, and start treatment when it is truly needed.

For senior dogs, heart health is a major part of longevity care. A heart murmur is not something to panic about, but it is also not something to ignore. Early detection gives owners and veterinarians more time to make good decisions.

For more helpful resources, explore other articles on senior dog care, heart health, nutrition, and preventive wellness.

Dr Kelly Yeo graduated from the University of Melbourne in 2009 and has extensive experience in companion animal medicine, with a special interest in geriatric care, chronic disease management, palliative care, and canine longevity.

Her work focuses on helping dogs live longer, healthier, and more comfortable lives through early detection, thoughtful nutrition, practical preventive care, and compassionate support for owners.