There are many types of heart disease that can affect your dog, and one of the more serious of these is a condition known as cardiomyopathy. There are several types of this fatal disease, and they are a major cause of irregular heartbeat (arrhythmia), congestive heart failure and sudden death. The two most common include a condition known as arrhythmogenic cardiomyopathy (ACM) and a second known as idiopathic dilated cardiomyopathy, or DCM. In many cases, the dog will develop ACM first, and then the condition will develop into DCM.

The term cardiomyopathy literally translates to "sick heart muscle." It occurs when the walls of the heart muscle become thin, weak and unable to contract properly. The left side of the heart is normally affected the most, but both sides can become enlarged. When this happens, the heart cannot pump blood efficiently to the rest of the body, causing the dog to become tired easily and to occasionally faint during any significant physical exercise. The heart's weakened pumping ability also causes fluid to build up in the lungs, the chest and/or abdominal cavities, and under the skin, leading to chronic pneumonia, congestive heart failure and a high risk for sudden cardiac death. Some animals also have cold noses and feet, plus pale gums, both of which are signs of poor circulation related to their cardiomyopathy.

All of these symptoms are usually accompanied by an ongoing arrhythmia. The condition is inherited in many animals, but also has been linked to infectious organisms including the ones that cause Lyme disease, bartonellosis and trypanosomiasis.

In canines, cardiomyopathy is seen mostly in purebred animals of the larger breeds, especially the Boxer. It's also found in the Afghan Hound, Doberman Pinscher, Great Dane, Irish Wolfhound, Newfoundland and Old English Sheepdog, as well as smaller breeds like the American Cocker Spaniel and English Bulldog. (In Cockers the cause is believed to be a deficiency in two specific amino acids, carnitine and taurine, which can usually be corrected through diet.) In most cases these conditions strike older dogs, and males are affected more often than females.

Cardiomyopathy is often an inherited condition. Sometimes it also can be caused by an electrolyte imbalance or medications for respiratory and thyroid disease, so your veterinarian will rule these out before diagnosing ACM or DCM. Diagnosis of the disease is made through a combination of physical exams, blood and laboratory tests.

Dogs with cardiomyopathy cannot be cured, and most die within six to 24 months after being diagnosed. However, in many animals, their symptoms may be successfully managed for a time if the disease is carefully treated with medications (such as beta blockers and digoxin), combined with lifestyle changes, including tight control of the animal's diet and exercise. The response to treatment can vary widely from dog to dog, but as with most serious diseases, the sooner the diagnosis is made, the longer the dog will survive.