With more widespread application of EMB techniques, a significant percentage of ICCM patients have been found to have lymphocytic myocarditis on biopsy. It is now appreciated that patients with myocarditis may also present with isolated abnormalities of left ventricular diastolic function, dysrhythmias, and/or complaints of chest discomfort with normal coronary angiograms. Epidemiologic and serologic data incriminate a viral etiology underlying many cases of acute myocarditis and ICCM. Although most cases of viral myocarditis appear to resolve without residual left ventricular dysfunction, a small but significant percentage of these patients progress to chronic congestive cardiomyopathy. In the absence of persistent active viral infection in these patients, myocardial damage may be mediated by both cellular and humoral immune mechanisms. The concept of virus-induced immune mediated myocardial damage forms the basis for attempts at immunosuppressive therapy. Whether immunosuppressive therapy alters the natural history of myocarditis is at present unknown and awaits demonstration by a controlled clinical trial.