Cardiomyopathy refers to disease of the heart muscle (the myocardium) without malformation of the heart or its valves. The term cardiomyopathy literally means "sick heart muscle." There is a breed predisposition to dilated cardiomyopathy in giant breeds, as well as in Doberman pinschers and boxers. Dilated cardiomyopathy is not the most common cause of heart failure in dogs in general. However, this is the most common cause of heart failure in large breeds of dogs. Small breeds are only occasionally affected. The most commonly affected breeds are Boxers, Doberman Pinschers, and Great danes. Occasionally, medium sized breeds, notably Cocker Spaniels and English Springer Spaniels, are also affected. Cardiomyopathy can also develop as a result of some toxins or infections. Heart failure occurs when the blood returning to the heart from the rest of the body cannot be pumped out fast enough to meet the demands of body tissues. Heart muscle disease is one of the potential causes of heart failure. Dilated cardiomyopathy is a condition characterized by a variety of changes in the heart muscle that result in pump failure. As the name implies, the heart chambers are usually dilated or enlarged, and the heart muscle itself is usually thin and weak, contracting with much less vigor than normal. The heart works harder to compensate for the loss of contractility, eventually leading to congestive heart failure. The abnormalities in the heart muscle cells give rise to irregular heart rhythms which may cause sudden death so proper petsafe is necessary.

Dilated cardiomyopathy is by far the most common type in the dog. There is dilation of the chambers of the ventricles of the heart with some increase (hypertrophy) in the heart muscle mass, and a loss of the normal contracting abilities of the ventricles. Dilated cardiomyopathy, or DCM, occurs when the heart muscle is thin, weak, and does not contract properly. DCM most commonly affects large or giant purebred dogs, but it also can be seen in smaller breeds such as cocker spaniels, and in mixed breed dogs. The condition can lead to congestive heart failure, in which fluid accumulates in the lungs, the chest or abdominal cavities, or under the skin. Because of reduced blood flow to the rest of the body, DCM also can result in weakness, fainting, and exercise intolerance. Abnormal heart rhythms, or arrhythmias, frequently accompany DCM, and can complicate the treatment of dogs with this disease. It is also common for dogs with DCM to show signs of both right and left heart failure. These signs can include weakness and exercise intolerance, and difficulty breathing with increased activity. Weight loss is common in dogs with DCM that do not retain fluid. Some animals exhibit signs due to reduced blood flow to tissues, including pale mucous membranes, bluish color to the mucous membranes, and cold feet and legs. Fainting may occur if abnormal heart rhythms are present, or if the heart's output is severely reduced. Hypertrophic cardiomyopathy is a form of cardiomyopathy, there is a tremendous increase in the mass of the heart muscle in the ventricles, with a resultant decrease in chamber size. Relatively few cases of hypertrophic cardiomyopathy in dogs have been reported, and no significant breed predisposition has been identified. Most of the dogs affected have been male.

Blood and urine tests do not give direct information about heart function, but they allow an understanding of other disorders in the body that may impact on heart function and treatment of heart disease. Chest radiographs (x-rays) provide the best look at the lungs and a view of the size and shape of the heart. In most cases, dilated cardiomyopathy causes tremendous enlargement of the heart. These changes are usually very apparent on x-rays.lectrocardiogram (ECG or EKG) is an assessment of the electrical activity of the heart. It accurately determines the heart rate and to more accurately identify any arrhythmias which might be present. Ultrasound examination (Sonogram, Echocardiogram) uses sound waves which bounce off the structures of the heart and are read on a TV-like monitor. It gives the most accurate determination of the size of each heart chamber, and permits measurement of the thickness of the heart walls. This is seen on the monitor in actual time so the contractions of the heart can be evaluated. Certain measurements can be taken which allow the actual strength of the heart's contraction to be measured as a number and compared to the normal animal. Ultrasound may not be available in all private veterinary practices because of the additional training needed to learn how to perform the examination and because of the cost of the equipment.

If the dog has a sudden onset of heart failure, rapid administration of the proper drugs is essential to survival. The following drugs may be used at various stages of treatment. Diuretics drugs stimulate the kidneys to remove excess fluid from the body. Furosemide is most commonly used, although others will be selected in certain circumstances. Nitroglycerin drug is called a venodilator; it dilates the veins throughout the body, especially the ones going to the heart muscle. It decreases the amount of blood returning to the heart by allowing some of it to pool in the veins. This takes some of the workload off the heart. This drug can be very useful for treating pulmonary edema, but it is only effective for a few days. Digitalis drug improves heart function in several ways. It regulates excess hormones that have been released, slows the heart rate, and strengthens each contraction of the heart. Enzyme blockers is a relatively new class of drugs which can directly block the compensation system that has gotten out of control. Vasodilators drugs dilate the arteries and/or the veins of the body so that the heart doesn't have to generate as much pressure to eject blood. They may be used long-term because they continue to be effective, as opposed to the short-term effects of nitroglycerin. Dogs treated with these drugs should be carefully watched for toxity and needs enough rest on pet beds. Loss of appetite, vomiting, diarrhea, and lethargy should be reported to the veterinarian immediately.