Dilated cardiomyopathy (DCM) is a disease of the heart muscle that is characterized by an enlarged heart that does not function properly. With DCM, both the upper and lower chambers of the heart become enlarged, with one side being more severely affected than the other. When the ventricle, or lower chamber, becomes enlarged, its ability to pump blood out into the lungs and body deteriorates. When the heart’s ventricle does not pump enough blood into the lungs, fluid begins to accumulate in the lungs. An enlarged heart soon becomes overloaded, and this often leads to congestive heart failure (CHF).