Heart valve malfunction in dogs (mitral insufficiency)

Image by Mirko Sajkov on Pixabay.
Image by Mirko Sajkov on Pixabay.

Many dogs slowly develop degenerative thickening and progressive deformity of one or more heart valves as they age. In time, these changes cause the valve, most commonly the mitral valve, to leak. While it can lead to heart failure, many dogs with the condition never show signs of the disease outside of a loud heart murmur.

What is the mitral valve?

The mitral valve separates the blood collecting chamber (left atrium) from the pumping chamber (left ventricle) leading to the body. In dogs with a heart valve malfunction, the volume of blood that leaks back into the atrium with each heartbeat tends to increase slowly over time.

What dogs are at the highest risk of heart valve malfunction?

Heart valve malfunction primarily affects older, small- to medium-sized dogs, although any dog can be affected. It is more common in some breeds, such as Cavalier King Charles spaniels and dachshunds.

What are the symptoms of heart valve malfunction?

Early in the disease process, your veterinarian may hear a soft murmur when the affected valve starts to leak. There usually is no noticeable change in the dog’s activity level or behavior for a long period of time.

Gradually, though, the valve leak tends to get worse, and the heart slowly enlarges. If the leak becomes severe, blood may start to back up behind the heart – usually into the lungs. This causes lung congestion and fluid accumulation (edema). When lung congestion and edema occur, congestive heart failure is present.

Reduced exercise ability may be the first sign of heart failure. Most dogs with heart failure caused by degenerative valve disease show signs of “left-sided” congestive failure. These signs include tiring quickly, increased breathing rate or effort for the level of activity, excessive panting, and cough (especially with activity). The presence of any of these signs should prompt a visit to your veterinarian to determine if heart failure (or another disease) has developed. 

More advanced signs of heart failure could include labored breathing, reluctance to lie down, inability to rest comfortably, worsened cough, reduced activity, and loss of appetite. Your veterinarian should be consulted right away if these signs occur.

Some dogs that become symptomatic from their heart disease develop fluid in the abdomen (ascites); others have episodes of sudden weakness or fainting that can result from irregular heartbeats or other complications. As long as no sign of heart failure develops, no treatment is necessary, although reduction of dietary salt intake is often advised.

How is a heart valve malfunction treated?

There are many dogs with degenerative valvular disease that never progress to heart failure, however, the condition is slowly progressive over years and is non-reversible. If heart failure develops, several medications and other strategies are used to control the signs. Since the disease tends to be progressive, the intensity of the therapy (including the number of medicines and dosages used) usually must be increased over time. Therapy is always tailored to the needs of the individual patient.

How is a heart valve malfunction treated?

If your dog is showing any symptoms of a heart valve malfunction, you should contact your veterinarian or the WSU Veterinary Teaching Hospital at 509-335-0711.

The Cardiovascular System of a Dog

The cardiovascular system includes the heart and blood vessels and performs the function of pumping and carrying blood to the rest of the body. The blood contains nutrients and oxygen to provide energy to allow the cells of the body to perform work.

Artist drawing of the inside of a dog heart with labels for the valves, ventricles, papillary muscles, septum, chorda tendinea and left ventricle free wall.
Artist drawing of the outside of a dog heart with labels for the atriums, ventricles, aortic arch, pulmonary artery, and coronary vessels.

The pictures in this section are reprinted with permission by the copyright owner, Hill’s Pet Nutrition, from the Atlas of Veterinary Clinical Anatomy. These illustrations should not be downloaded, printed or copied except for personal, non-commercial use.

This information is not meant to be a substitute for veterinary care. Always follow the instructions provided by your veterinarian. Washington State University assumes no liability for injury to you or your pet incurred by following these descriptions or procedures.