Cardiac mortality is more frequent in diabetic patients than in normal subjects and particularly heart failure occurs 4-6 times more frequently in these patients than in normals also excluding diabetics with coronary artery disease (CAD). To study cardiac function, 20 patients with type II diabetes mellitus (11 M and 9 F, mean age 48 +/- 9 years), and 13 normal subjects (6 M and 7 F, mean age 48 +/- 13 years), were submitted to radionuclide ventriculography with technetium 99m to evaluate some indices of cardiac function at rest and during effort. The diabetic patients were on good metabolic control testified by a satisfactory fasting and post prandial glycaemia, absence of glycosuria in the last 3 monthly controls and a normal value of glycosylate haemoglobin; they had no vascular or neurological complications; CAD was excluded submitting these patients to a maximal effort ECG on an ergometer. The normal subjects were comparable to diabetic patients for age, sex, mean arterial pressure, body mass index and body surface area. At rest, stroke volume, peak filling rate, cardiac output, ejection fraction (EF), were significantly lower in diabetic patients than in normal subjects. Systemic vascular resistances (SVR) were higher in diabetics than in normal subjects (p less than 0.01). Mean EF during effort increased in both normals and diabetics but 30% of diabetic patients showed no increase in EF during effort (less than 5%). Preload, represented by end-diastolic volume or blood volume, did not differ in the 2 groups.(ABSTRACT TRUNCATED AT 250 WORDS)