Myocarditis is a disease in which an inflammatory infiltrate develops within the muscle layer of the heart. This results in damage or necrosis of the cardiomyocytes, or heart muscle cells. The most common cause of this disorder is infectious agents. The disease can occur in isolation or as a dangerous complication of other infectious diseases, such as pharyngitis or sinusitis. The condition affects every age group, from newborns to the elderly, but the clinical picture varies considerably in different age groups.