This disease is caused by a weakening of the heart muscle. It primarily affects the left ventricle, the heart's main pumping chamber. In a heart with dilated cardiomyopathy, the diseased muscle fibers have stretched and the chamber has enlarged to make up for its lost pumping power. A heart affected by dilated cardiomyopathy has difficulty supplying enough blood flow to meet the body's needs. This can result in heart failure.