The aim of this study was to compare, by gated radionuclide angiography, systolic and diastolic ventricular function in insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) diabetic patients without overt cardiovascular disease. The study population consisted of 20 IDDM patients (15 male, 5 female; 40.7 ± 10.3 years), 14 NIDDM patients (9 male, 5 female; 47.0 ± 7.5 years) and 12 healthy subjects (7 male, 5 female; 41.5 ± 6.3 years) as a control (C) group. The duration of diabetes (DD) and glycosylated hemoglobin (HbA<sub>1c</sub>) levels were significantly higher in the IDDM patients. The ventricular ejection fraction and peak ejection rate (PER) were assessed by gated radionuclide left ventriculography and were similar in three groups, while the peak filling rate (PFR) was lower in the NIDDM patients compared to the IDDM patients (p < 0.05) and controlled healthy subjects (p < 0.01, IDDM = 3.39 ± 1.14; NIDDM = 2.65 ± 0.83; C = 3.55 ± 0.73), the time to PFR was significantly more prolonged in the NIDDM group than in the IDDM (p < 0.05) and C groups (p < 0.05, NIDDM = 162 ± 26; IDDM = 140 ± 28; C = 142 ± 23). The PFR/PER ratio was near the normal value (-1) in the IDDM patients and controlled subjects, while in the NIDDM patients it was reduced ( = 0.84 ± 0.18). Seven IDDM and 4 NIDDM patients had borderline signs of cardiovascular autonomic neuropathy, unrelated to DD, HbAic and scintigraphic parameters. Left ventricular systolic performance was substantially normal and similar in both the IDDM and NIDDM patients. Ventricular diastolic filling was impaired in the NIDDM patients, as shown by the decrease in PFR and in particular in the PFR/PER ratio. Our radionuclide data suggest that the NIDDM patients had a prevalent abnormality of ventricular diastolic performance, with respect to the IDDM patients, although the latter patients had higher DD and HbA<sub>1c</sub> values.