The heart is a remarkably durable and efficient pump that provides all cells of the body with nutrients and removes waste products. Myocarditis is a process characterized by an inflammatory infiltrate of the myocardium with necrosis and/or degeneration of adjacent myocytes not typical of the ischemic damage associated with coronary artery disease. Autoimmune heart disease following viral infection involves the production of key cytokines by immune cells such as macrophages and natural killer cells. Finally, if environmental or genetic factors allow overproduction of proinflammatory cytokines, then progression to chronic autoimmune myocarditis may follow. Importantly, myocarditis often precedes the development of dilated cardiomyopathy, which can lead to heart failure and the need for cardiac transplantation.