Among the many diseases that can strike the human and canine heart is a disease of the heart muscle itself. Dilated cardiomyopathy, or DCM, causes the walls of the heart's four chambers to become enlarged and thus not function properly, and it usually is found in larger breeds of dog.

Most cases of DCM show up in middle-aged and older dogs, with the average age of onset being anywhere between four and 10 years. It's believed to have a genetic trigger, but the actual cause of the disease isn't yet known. Breeds affected most often include the Boxer, Doberman Pinscher, Golden Retriever, Irish Wolfhound, Labrador Retriever, Newfoundland and Scottish Deerhound.

With dilated cardiomyopathy both the left and right sides of the heart are affected; but one side is usually more severely impacted than the other. Deterioration of the heart muscle causes the upper and lower chambers of the heart (the atria and ventricles, respectively) to enlarge, weakening the ventricles and making them less able to pump blood. When this happens, blood pools in the body and fluid backs up into the lungs, abdomen and other areas in the body.

As dogs age, the signs of cardiomyopathy may appear and should be reported to your veterinarian right away. These include heavy or labored breathing, extreme lethargy, coughing, fainting spells and/or restlessness.
Most dogs with severe DCM do not survive longer than a few weeks or months. In dogs whose condition is not as advanced, however, medications can be prescribed to help improve the animal's heart function, prevent fluid buildup and boost its overall quality of life. The most commonly prescribed of these medications are Lanoxin (generically known as digitalis or digoxin), which is used to improve the heart's pumping action, and diuretics like Lasix (Furosemide). The latter is used to prevent fluid from accumulating in and around the lungs, which can lead to life-threatening pneumonia. How scrupulous the owner is about administering their pet's medication and scheduling regular checkups will go a long way toward determining how long a dog with DCM will survive.
In some cases, dogs with dilated cardiomyopathy also may develop an irregular heartbeat, known as a cardiac arrhythmia. This potentially life-threatening complication is the result of an electrical disturbance within the heart. Owners whose dogs have a heart arrhythmia are urged to purchase an inexpensive stethoscope and keep a daily journal of their dog's heart rate and rhythm. Any documented increase or decrease in your dog's heart rate, plus any irregular heartbeats, can then be shared with your veterinarian to determine the best course of treatment.