Myocarditis is a caused by inflammation of the heart muscle. It may be a complication during or after various viral, bacterial, or parasitic infectious diseases, such as polio, influenza, rubella, or rheumatic fever. The most common cause is a viral infection , and the most common virus being an enterovirus. Over many years, a chronic enterovirus heart infection and the body’s response to that infection can lead to irreversible heart muscle damage and heart failure. Some cases of myocarditis may progress to congestive heart failure. Myocarditis is often caused by various diseases such as syphilis, goiter, endocarditis, or hypertension. It may appear as a primary disease in adults or as a degenerative disease of old age. It can contribute to dilation (enlargement due to weakness of the heart muscle) or hypertrophy (overgrowth of the muscle tissue).

In acute myocarditis, individuals may experience fever, as well as the symptoms of chronic myocarditis, i.e. chest pains, palpitations, shortness of breath and fatigue.