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What is Mitral Valve Disease?

Chronic Degenerative Mitral Valve Disease (CDVD) is the most common cause of cardiac disease in dogs. Though it can affect young dogs, the vast majority of patients with mitral valve disease are older dogs. Mitral valve disease is also the most common cause of congestive heart failure in small breed dogs.

To better understand how the changes that occur with CDVD affect the normal function of your pet’s heart it is important to understand how the normal heart  works

Chronic Degenerative Valve Disease

In some dogs the collagen in the heart valves begins to degenerate over time.  We are not sure why this happens in some dogs and not others, but it is likely that this disease has a genetic basis. This degeneration of valve tissue most commonly affects the mitral valve, though it can affect others as well.

As the tissue in the valve degenerates and shrinks, small round nodules are formed on the edges of the valve leaflets (figure). This means that instead of coming together and creating a tight seal, there are now gaps between them. When the powerful left ventricle squeezes blood out through the aorta, some of that blood can now flow backwards into the left atrium through these gaps. This backwards flow of blood is called regurgitation. Over time, the valve continues to degenerate and the gaps between the valve leaflets grow larger, causing more and more regurgitation.

Remember that blood arriving into the left atrium is coming from the lungs. A traffic jam develops when regurgitated blood fills the left atrium instead of blood from the lungs. Over time, this induces congestion in the lungs and causes them to accumulate fluid. If this happens, the patient is said to be in heart failure.

It is important to realize that this disease process usually occurs gradually over several years. Most animals can compensate for the disease for a long period of time and be asymptomatic for years. Some dogs never show signs of heart problems and never need treatment. However, once we identify a patient with this disease, regular monitoring is essential so that we can begin medication as soon as the patient starts to show symptoms.

Treating Mitral Valve Disease

No treatment is needed until a patient starts to show signs. Regular monitoring allows us to start treatment as soon as it becomes necessary. By starting treatment early, we can maximize your pet’s quality of life for as long as possible. In patients with CDVD and signs of heart failure, it is common for your veterinarian to prescribe a combination of drugs. Therapy is aimed at maximizing the heart’s efficiency at pumping blood to the body.

If your pet has an arrhythmia, or abnormal electrical activity within the heart, your cardiologist might prescribe drugs such as digoxin or diltiazem to change the way the heart beats.

Continuing to monitor your pet’s symptoms and communicating with your veterinary team is extremely important in these cases. Since this disease is constantly changing, it is common for an individual pet to need different doses of different drugs over the course of its life. With your help, your cardiologist can identify which changes need to be made as early as possible. If your pet is experiencing worsening symptoms, please contact us right away so that we can ensure the optimal therapy for your pet.


It is difficult to predict the life expectancy for any individual patient with this disease. Some dogs live for years with no or mild symptoms, while some dogs rapidly worsen and only live for a few months. Complications such as rupture of chordae tendinae (these structure sustain the mitral valve apparatus), or developing high pressure in the lung (pulmonary hypertension) can worsen the prognosis. Other possible factors influencing the prognosis include how severe your pet’s disease is when it is diagnosed, your pet’s response to medications, and whether any other diseases (such as kidney problems) are also present in your pet.

Degenerative mitral valve Normal mitral valve

Severe affected mitral valve (left). Mitral valve leaflets are very thick compare to those from a normal mitral valve (right).