A variety of disciplines including noninvasive and invasive cardiac methodologies, as well as epidemiologic studies, have provided information that has altered our view on the relation of diabetes to cardiac disease. Instead of an exclusive focus on coronary artery disease, it is now recognized that heart muscle can be independently involved in diabetic patients. In diabetics without known cardiac disease, abnormalities of left ventricular mechanical function have been demonstrated in 40 to 50% of subjects, and it is primarily a diastolic phenomenon. Left ventricular hypertrophy may eventually appear in the absence of hypertension. The diastolic dysfunction appears related to interstitial collagen deposition, largely attributable to diminished degradation. The presence of even moderate obesity intensifies the abnormality. Reversibility of this process is not readily achieved with chronic insulin therapy. Experimental studies have indicated normalization of the collagen alteration by endurance training, begun relatively early in the disease process. General measures of management include the control of other cardiac risk factors and a reasonable program of physical activity. The high mortality during an initial acute myocardial infarction has been attributed to heart failure, which is managed as in nondiabetic patients. Recently, the early introduction of aspirin, thrombolysis, and beta-adrenergic blockade has reduced mortality during the initial infarction. Chronic use of the latter agent over the subsequent years has also proven to be more beneficial in diabetic patients with acute myocardial infarction compared with nondiabetic patients.