In subclinical diabetic cardiomyopathy, previous reports did not positively correlate the altered cardiac performance with metabolic parameters. Fifteen insulin-dependent diabetic subjects, without any clinical or instrumental evidence of heart diseases, were studied. Signs of diabetic microangiopathy were absent. Systolic time intervals, metabolic and hormonal parameters (blood glucose, free fatty acids, blood lactate and plasma norepinephrine) were evaluated at rest and after dynamic exercise during poor (MAGE 6.36 +/- 0.72 mmol/l) and good (MAGE 3.46 +/- 0.66 mmol/l) metabolic control, obtained by means of insulin therapy. Rest values of systolic time intervals were normal during poor and good metabolic control. After exercise, pre-ejection period/left ventricular ejection time ratio increased mainly during poor control as a result of an increased pre-ejection period: conversely, a smaller increase in pre-ejection period/left ventricular ejection time ratio occurred during good metabolic control. The exercise induced free fatty acids utilization did not occur during poor control as it occurred during good control. The percentage of increments in blood lactate was virtually identical in ketotic and non-ketotic patients and in normal subjects. High norepinephrine plasma levels were observed both at rest and during dynamic exercise in poorly controlled diabetic patients. Conclusively, testing of systolic time intervals after exercise might be useful in the detection of preclinical diabetic cardiomyopathy. The decreased cardiac functional reserve observed during poor control might be related to an altered energetic fuel utilization.