The heart has four chambers, two atria, two ventricles, with a valve existing between each atrium and ventricle on each side. Blood flows in one direction through the heart – from the right atrium, to the right ventricle, and to the lungs. It flows back through the heart from the left side, from the left atrium to the left ventricle, and is pushed out to the rest of the body. The valve between each atrium and ventricle exist for one purpose, to keep blood from being pushed back into the atria, maintaining a one-directional flow of blood. Valve regurgitation is the name given to ‘leaky valves’, also known as a heart murmur. A murmur is heard on auscultation of the chest with a stethoscope. The sound heard is a result of turbulence created when the blood is pushed back through the leaky valve to the left atrium.

Congestive heart failure is a direct result of a mitral heart regurgitation. In a healthy heart, the left ventricle is well muscled, and a healthy valve means all the blood is directed to the body and the tissues. In a pet with mitral valve regurgitation, the force of the contraction from the ventricle is too strong and the blood is pushed forcefully in the wrong direction, pushing blood back to the lungs. This causes congestion, and fluid pools in the lungs, resulting in breathing difficulty.