The cardiomyopathies are usually classified as dilated, hypertrophic, or restrictive. Although clinical presentations vary among these myopathies, systolic or diastolic dysfunction characterizes the principal pathophysiologic features of each. Advances in genetic linkage analysis and mutation screening have recently allowed investigators to establish a genetic basis for several forms of dilated and hypertrophic cardiomyopathy. Although traditional treatment modalities and newer strategies (such as atrioventricular pacing in patients with dilated cardiomyopathy and pacing or amiodarone therapy for patients with hypertrophic cardiomyopathy) may provide short-term relief, cardiac transplantation may be the only intervention that can alter the natural history and poor prognosis for these potentially lethal conditions. Myocarditis, which usually presents as an acute form of dilated cardiomyopathy, may have a broad spectrum of presentation and is currently treated with nonspecific supportive measures. Although the polymerase chain reaction may provide rapid diagnosis of viral etiologies, newer therapies have not yet been developed. Clinical trials with intravenous immunoglobulin, however, are currently in progress. In patients whose symptoms do not resolve, cardiac transplantation may afford the only potential for long-term survival.