Degenerative Valve Disease
The valves between the top chambers of the heart (the atria) and the bottom chambers (the ventricles) include the mitral valve on the left side of the heart and the tricuspid valve on the right side of the heart. These valves prevent blood from flowing backward into either the left or right atria when the ventricles contract. The valve leaflets can degenerate and become abnormally shaped with age resulting in improper closure of the valve. The valves become "leaky" and this abnormal, backwards flow of blood leads to a heart murmur.
The heart will enlarge to maintain the forward flow of blood in the face of a leaky valve. Some dogs with long term valve degeneration will develop fluid build-up in their lungs or congestive heart failure. An echocardiogram, a heart ultrasound, is needed to accurately diagnose degenerative valve disease and classify the disease as mild, moderate, or severe. Other diagnostic tests that are commonly utilized in patients with degenerative valve disease include thoracic radiographs and measurement of blood pressure.