The incidence of mortality from cardiovascular disease is higher in diabetic patients. The objective of the present investigation was to test the hypothesis that the diabetes-induced depression in cardiac function may be due to hypertriglyceridemia. Hyperlipidemia and a depressed left ventricular developed pressure and rate of increase and decrease of ventricular pressure (+/- dP/dt) were produced in isolated hearts from rats made diabetic with streptozotocin compared with hearts from control animals. This depressed cardiac performance was successfully prevented by hydralazine treatment (for 3 weeks), which also lowered plasma triglyceride levels and suggested that hyperlipidemia may be important in altering cardiac function in experimental diabetic rats. The beneficial effects of clofibrate, verapamil, prazosin, enalapril, and benazepril administration were then studied in diabetic rats. The treatments (with the exception of enalapril) significantly reduced plasma triglyceride levels but did not prevent the onset of heart dysfunction in chronically diabetic rats. These studies suggest that in the chronically diabetic rat, hypertriglyceridemia may not be as important as previously suggested, in the development of cardiac dysfunction. Since acute dichloroacetate perfusion improves cardiac function in 6 week (but not 24 week) diabetic rats, it appears more likely that improving myocardial glycose utilization is more critical than triglyceride lowering, in preventing cardiac dysfunction in the diabetic rat at this time point.