the best cardiac doctors near me Myocarditis Myocarditis is a disease marked by inflammation and damage of the heart muscle. Although the exact incidence of myocarditis is not known, it is estimated that several thousand patients per year are diagnosed in the United States. Myocarditis usually attacks otherwise healthy people. It is believed that 5 to 20% of all cases of sudden death in young adults are due to myocarditis. There are many causes of myocarditis, including viral infections, autoimmune diseases, environmental toxins, and adverse reactions to medications. The prognosis is variable but chronic heart failure is the major long term complication.