Myocarditis is inflammation of the muscles of the heart. It is a rare but serious complication of many illnesses, although it is usually caused by a viral infection, most commonly parvovirus. However, it can also be caused by parasites, bacteria, fungus, allergies and toxins. In most of the world, Chagas disease is the leading cause. It can also be the result of an autoimmune response. It is often accompanied by pericarditis. It is one of the leading causes of sudden death in otherwise healthy adults (accounting for about 20% of sudden deaths in this age group) and is often either the direct cause or a contributing cause to the death of patients with AIDS.