Dilated cardiomyopathy or DCM, also known as congestive cardiomyopathy, is a condition in which the heart becomes weakened and enlarged, and cannot pump blood efficiently. The decreased heart function can affect the lungs, liver, and other body systems.

DCM is one of the cardiomyopathies, a group of diseases that primarily affect the myocardium (the muscle of the heart). Different cardiomyopathies have different causes, and affect the heart in different ways. In DCM a portion of the myocardium is dilated, often without any obvious cause. Left and/or right ventricular systolic pump function of the heart is impaired, leading to progressive cardiac enlargement and hypertrophy, a process called remodeling.

Dilated cardiomyopathy is the most common form of cardiomyopathy. It occurs more frequently in men than in women, and is most common between the ages of 20 and 60 years. About one in three cases of congestive heart failure (CHF) is due to dilated cardiomyopathy. Dilated cardiomyopathy also occurs in children.