Heart Valve Malfunction in the Dog (Mitral Insufficiency)
This information is not meant to be a substitute for veterinary care.
Always follow the instructions provided by your veterinarian.
Anatomy of the heart of a dog
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 to leak. The mitral valve is most
commonly affected. This valve separates the blood collecting chamber (left
atrium) from the pumping chamber (left ventricle) leading to the body. Some
dogs also develop these changes in the tricuspid valve, which
separates the collecting (right atrium) and pumping (right ventricle)
chamber leading to the lungs.
Certain breeds have an inherited predisposition to this
disease. Degenerative valvular disease is slowly progressive over years and
is non-reversible. The volume of blood that leaks back into the atrium with
each heartbeat tends to increase slowly over time. However, many dogs with
this disease never develop signs of congestive heart failure even though
they may have a loud murmur. 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. Again, there are
many dogs with degenerative valvular disease that never progress to heart
However, if heart failure develops, several medications and other strategies
are used to control the signs. Since the disease is not reversible and heart
failure, when it occurs, 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.
This Pet Health Topic was written by
O. L. Nelson, DVM, MS,
Diplomate ACVIM (Cardiology & Internal Medicine) Washington State
Washington State University assumes no liability for injury
to you or your pet incurred by following these descriptions or
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