Dilated cardiomyopathy is a moderately common syndrome resulting from many causes, many of which are yet to be defined. The syndrome is relatively easy to diagnose in its late congestive stage if valvular abnormality, hypertensive disease, and gross myocardial infarction are absent. However, it should be suspected in patients with undiagnosed chest pain, in patients whose severe arrhythmia has no obvious cause, and in any patient with demonstrable ventricular dilatation or systolic malfunction. It may follow infections, especially viral ones and is found in many deficiency diseases, especially diabetes. Repeated episodes of angina due to epicardial disease may result in myocardial "stunning" with ultimate dilation and failure. Microvascular spasm or occlusion may be etiologically important. Dilated cardiomyopathy may be a manifestation of toxins, with ethanol being the most important. Immune mechanisms may play a major role, either independently or in connection with other factors. Early diagnosis may be made with the help of echocardiography, radionuclide angiography, and even coronary arteriography. Gallium scan may be helpful, and if positive myocardial biopsy is indicated. Therapy includes classic measures for congestive failure if it is present: cardiac glycosides, diuretics, antiarrhythmics, and anticoagulants. There is evidence that vasodilators, calcium channel blockers, and beta-adrenergic blockers may be helpful for both general and specific reasons, but these should be used with care. Prednisone and azathioprine may help if there is an inflammatory component. Cardiac replacement remains an ultimate measure.