Dilated cardiomyopathy is a disease of the heart muscle, usually starting in your heart's main pumping chamber (left ventricle). The disease occurs when the heart's ability to pump blood is lessened because its left ventricle, is enlarged and weakened.

The ventricle stretches and thins (dilates) and can't pump blood as well as a healthy heart can. The term "cardiomyopathy" is a general term that refers to the abnormality of the heart muscle itself.