The myocardium is the muscle wall of the heart or heart muscle. It contracts to pump blood out of the heart and then relaxes as the heart fills with the returning blood. The outer serous membrane of the myocardium is called the “epicardium.” The membrane that covers its interior is called “endocardium”.

Myocarditis is an inflammation of the myocardium. When the heart becomes inflamed, it can not pump as effectively due to the swelling (edema) and the damage suffered by its cells. The heart muscle can be further damaged if the immune system sends antibodies to try to fight the cause of the inflammation. Sometimes these antibodies attack the tissues of the heart instead. If too many cells of the heart muscle are damaged, it weakens. In some cases, this process is very fast and results in heart failure or even sudden death.