Dilated Cardiomyopathy (DCM):
https://www.vetmed.wsu.edu/outreach/Pet-Health-Topics/categories/diseases/dilated-cardiomyopathy-in-dogs
This information is not meant to be a substitute for veterinary care. Always follow the instructions provided by your veterinarian.

What is it?
DCM is a disease of the heart muscle that results in weakened contractions and poor pumping ability. As the disease progresses the heart chambers become enlarged, one or more valves may leak, and signs of congestive heart failure develop. The cause of DCM is unclear in most cases, but certain breeds appear to have an inherited predisposition. Large breeds of dogs are most often affected, although DCM also occurs in some smaller breeds such as cocker spaniels. Occasionally, DCM-like heart muscle dysfunction develops secondary to an identifiable cause such as a toxin or an infection. In contrast to people, heart muscle dysfunction in dogs and cats is almost never the result of chronic coronary artery disease (“heart attacks”).

What are the signs of this disease?
Early in the disease process there may be no clinical sign detectable, or the pet may show reduced exercise tolerance. In some cases, a heart murmur (usually soft), other abnormal heart sounds, and/or irregular heart rhythm is detected by your veterinarian on physical examination. Such findings are more likely as the disease progresses. As the heart’s pumping ability worsens, blood pressure starts to increase in the veins behind one or both sides of the heart. Lung (pulmonary) congestion and fluid accumulation (edema) often develop behind the left ventricle/atrium. Fluid also may accumulate in the abdomen (ascites) or around the lungs (pleural effusion) if the right side of the heart is also diseased. When congestion, edema and/or effusions occur, heart failure is present. Weakness, fainting episodes, and unfortunately, even sudden death can result from heart rhythm disturbances (even without “heart failure” signs).

What are the signs of heart failure?
Dogs with heart failure caused by DCM often show signs of left-sided congestive failure. These include reduced exercise ability and tiring quickly, increased breathing rate or effort for the level of their activity excess panting, and cough (especially with activity). Sometimes the cough seems soft, like the dog is clearing its throat. Poor heart pumping ability and arrhythmias can cause episodes of sudden weakness, fainting, or sudden death as noted above. Some dogs with DCM experience abdominal enlargement or heavy breathing because of fluid accumulation in the abdomen or chest, respectively. Presence of any of these signs should prompt a visit to your veterinarian to determine if heart failure (or another disease) has developed. More advanced signs of heart failure could include labored breathing, reluctance to lie down, inability to rest comfortably, worsened cough, reduced activity, loss of appetite, and collapse. A veterinarian should be consulted right away if these signs occur. Signs of severe heart failure may seem to develop quickly with DCM, but the development of underlying heart muscle abnormalities and progression to overt heart failure probably takes months to years.

How is this disease diagnosed?
A cardiac exam by a veterinarian can detect abnormal heart sounds (when present) and many signs of heart failure. Usually chest radiographs (x-rays), an electrocardiogram (ECG), and echocardiogram are performed to confirm a suspected diagnosis and to assess severity. Echocardiography also can be used to screen for early DCM in breeds with a higher incidence of the disease. Resting and 24-hour (Holter) ECGs are sometimes used as screening tests for the frequent arrhythmias that usually accompany DCM in some breeds, especially boxers and Doberman pinchers.

What can be done if my pet has this disease?
Asymptomatic (subclinical) cases of DCM may be treated with enalapril or another ACE inhibitor to slow progression of the changes leading to heart failure. Other medications and strategies are also used as signs of heart failure develop and/or if rhythm abnormalities are present. Therapy is always tailored to the needs of the individual patient. Since this disease is not reversible and heart failure tends to be progressive, the intensity of therapy (for example, the number of medicines and the dosages used) usually must be increase over time.

This Pet Health Topic was written by O. L. Nelson, DVM, MS, Diplomate ACVIM (Cardiology & Internal Medicine) Washington State University.
Washington State University assumes no liability for injury to you or your pet incurred by following these descriptions or procedures.