Forty-nine diabetic patients (26 type I and 23 type II), free of cardiovascular disease symptoms, were compared with 32 controls in a noninvasive study of left ventricular (LV) function. Absence of ischemic cardiopathy was confirmed by routine investigations and an exercise electrocardiogram using 12 leads with a thallium-201 myocardial scintigraphy. Diabetic patients had (1) a significantly prolonged mean isovolumetric relaxation time (IVRT) assessed by M-mode echocardiography and phonomechanography; (2) a significantly reduced E-F slope; (3) an increased mean Weissler index (pre-ejection period/LV ejection time). The IVRT and E-F slope abnormalities reflect increased myocardial stiffness and impaired LV compliance. The increased Weissler index reflects impaired myocardial contractility. These abnormalities were not related to sex, age, duration of diabetes or to the presence or extent of complications. No significant difference was found between diabetic patients and controls for mean diastolic and systolic LV diameters, thickness of the posterior wall or of the interventricular septum, assessed by echocardiography, or for the ejection fraction, determined by radionuclide angiocardiography. Finally, more than half of the patients with a frankly abnormal IVRT, Weissler index and E-F slope had had diabetes for less than 5 years, some even less than 2 years, without complications. These data show: (1) evidence of LV dysfunction specific to diabetes and unrelated to ischemic cardiopathy and hypertension; (2) the possible involvement of a metabolic factor in this early asymptomatic LV abnormality rather than microangiopathy.