Infectious myocarditis occurs when an infection, usually viral but sometimes bacterial, causes heart muscle to become inflamed after an autoimmune response. Disease-fighting cells from the body responding to the infection can enter the heart and release chemicals that may damage the heart muscle and cause inflammation, resulting in myocarditis. The heart then may become thick, swollen, and weak. There is a risk of heart failure with myocarditis. Myocarditis may often have no symptoms, but some potential signs include shortness of breath, chest pain, swelling of the ankles, and fatigue. In order to prevent or treat infectious myocarditis, seek immediate medical attention if you have an infection.