Myocarditis: Inflammation of the myocardium, the heart muscle.
Myocarditis can be caused by a number of different conditions. The most common cause is infection of the heart muscle by a virus. The virus causes the initial heart muscle inflammation. After the initial viral infection subsides, the body's immune system continues to inflict inflammatory damage on the heart muscles, prolonging the myocarditis, a process termed autoimmunity. Other causes of myocarditis include such as a disease called sarcoidosis, various autoimmune diseases such as systemic lupus, and certain drugs.