Cardiomyopathy

Blood enters the heart at the right atrium, where it is stored briefly before being pumped down into the right ventricle, which in turn pumps blood into the lungs. In the lungs, the blood receives oxygen before flowing back to the heart, this time to the left atrium. The blood stays in the left atrium for a few seconds before being pumped down into the left ventricle. From there, the blood is pumped throughout the rest of the body.

Valves regulate the flow of blood to help the heart work efficiently. These valves, located between the atrium and ventricle on each side of the heart, serve as doors between the two areas. When either atrium fills with blood, the valve between the atrium and the ventricle closes to prevent the blood from entering the ventricle prematurely. When the valve opens, the blood passes down to the ventricle; once the blood reaches the ventricle, the valve closes again to prevent blood from flowing back up into the atrium.

This movement of blood results from electrical impulses that are transmitted from the brain to the heart. The impulses not only direct the heart to beat in the first place, but also enable the heart to maintain a steady, regular rhythm. With Cardiomyopathy, however, the electrical impulses are disturbed, and the heart beats erratically, which is an arrhythmia.

Although there are several kinds of arrhythmias, the most common is called premature ventricular contraction (PVC). Instead of beating in a steady, regular rhythm, the ventricle contracts earlier than it should. The result is a heartbeat that does not have a corresponding pulse, unlike the normally functioning heart, where there is a pulse for every beat. Some experts characterize the malfunction as a stutter.

A dog with only occasional PVCs probably will not show any symptoms of heart disease. But if multiple, successive PVCs occur — what experts call a “run” of PVCs — the heart cannot produce a normal, effective contraction, which results in a stoppage of blood flow to the brain and other vital organs, causing a dog to collapse. A prolonged run of PVCs can lead to complete cardiac arrest and death, unless the heart resumes a normal pattern of contractions.

Sometimes a lack of adequate contractions causes a dog’s heart to swell to compensate for the inefficient pumping function. This results in congestive heart failure. Symptoms include coughing, labored breathing, lethargy and abdominal swelling.