Concurrent viral infection and myocarditis presumably indicate viral myocarditis. The electrocardiographic and pathologic changes developing during acute infection may, however, result from changes not produced by the infection itself, eg, fever, tachycardia, ischemia, potassium depletion, vitamin deficiencies, drugs. This qualification should be remembered in the evaluation of all alleged virus myocarditis. Viral infection seems to prefer the very young. Its localization in the heart is favored by general or local hypoxia, perhaps thus explaining a predilection for the subendocardium. It may be influenced by the strain of the organism or by the hormonal or immunologic state of the host. Intrauterine infection of the fetus with rubella, mumps, and perhaps coxsackievirus can induce congenital cardiac defects. The role of virus infection in precipitating acute myocardial infarction deserves further study. The value of treatment, including steroids, nonsteroidal immunosuppressive agents, and “antiviral” agents is not yet established.