Mitral Valve Insufficiency in Dogs (MVI)

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The mitral valve is between the upper and lower right chambers of the heart (atrium and ventricle). It's a one-way valve to keep blood from flowing the wrong direction.

What Is Canine MVI?

Usually, blood that's been through the body delivering oxygen to all the tissues returns to the right atrium, goes through the mitral valve to the right ventricle, and then gets pumped to the lungs to pick up more oxygen. Next, it goes over to the left atrium, then the left ventricle, and then out to the body to deliver oxygen again.

When mitral valve insufficiency is present, blood can leak backward out of the right ventricle into the right atrium.

MVI is a common form of heart disease in small and medium dog breeds.

Causes of Mitral Valve Insufficiency in Dogs

A dog's mitral valve may simply wear out over time. MVI can also be caused by ruptured chordae tendinae or infections of the heart valves (endocarditis). Endocarditis is commonly caused by dental infections.

Signs of Mitral Valve Insufficiency in Dogs

Dogs with MVI might have a heart murmur as their only sign. MVI doesn't cause any clinical signs early in its course, but over time, it progresses to congestive heart failure (CHF). The length of time it takes for MVI to cause CHF varies widely between individuals, but when it occurs, the signs can include exercise intolerance, weakness, coughing, and trouble breathing.

Sudden death is always a risk for dogs with MVI.

Diagnosis of MVI in Dogs

MVI is diagnosed through a combination of a physical exam, x-rays, and echocardiography. On physical exam, a heart murmur may be identified by a veterinarian. X-rays may show an enlarged left side of the heart and pulmonary edema (fluid in the lungs) once CHF develops.

Echocardiography is the most useful for identifying mitral valve insufficiency and determining its stage.

Treatment of Mitral Valve Insufficiency in Dogs

Veterinarians differ on when they feel treatment for MVI should start. While many medications don't do any good until the dog is in congestive heart failure, some newer cardiac drugs may help increase the time before CHF occurs. A veterinary cardiologist will have the most recent information on medicines and treatment strategies for MVI.

Some medications that may be used include:

• ACE inhibitors. These medications reduce blood pressure by dilating blood vessels, so it's easier for the heart to pump blood out to the body.
• Diuretics. These medications help remove the excess fluid that can build up in the body tissues (pulmonary edema and ascites) during congestive heart failure.
• Beta blockers. These medications lower blood pressure and reduce resistance to the heart's pumping.
• Inotropic drugs. These medications help strengthen the heart muscle. In dogs, the most common of is pimobendan (Vetmedin).
• Low salt diet. Restricting the intake of salt can help a dog's body reduce excessive fluid.

Heart treatment is lifelong for dogs with CHF due to MVI.

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