The present study compares the cardiovascular consequences of a 6-week fructose feeding in nondiabetic and streptozotocin-diabetic rats. Myocardial performance of these animals was determined using the isolated perfused working heart preparation. Systolic blood pressure, pulse rate, ventricular weight/body weight ratio, and plasma levels of glucose, insulin, triglycerides, and cholesterol were measured. In nondiabetic rats, fructose drinking caused significant increases in blood pressure, pulse rate, and plasma concentrations of insulin and triglycerides. Streptozotocin-diabetic animals exhibited significantly less body weight growth, slower pulse rate, higher plasma levels of cholesterol and triglycerides, ventricular enlargement, and functional impairment of the myocardium. The fructose-loaded diabetic rats had larger increases in plasma cholesterol and triglycerides than did control fructose-fed rats, but the fructose-induced increases in blood pressure and pulse rate were attenuated significantly. However, plasma levels of glucose and insulin and the degree of ventricular enlargement and myocardial dysfunction were not significantly different from those of control diabetic rats. These results show that fructose loading for 6 weeks can cause increases in blood pressure, pulse rate, and plasma lipids in both nondiabetic and diabetic rats. However, fructose ingestion does not significantly alter glycemic control or affect the development of myocardial dysfunction in streptozotocin-diabetic rats.