To determine whether left ventricular (LV) filling abnormalities in diabetes are associated with diabetic microangiopathy, and to evaluate the effect of a short-term glycemic control on the filling abnormalities, diastolic filling dynamics were assessed by pulsed Doppler echocardiography in 246 patients with non-insulin-dependent diabetics. Isovolumic relaxation time and the ratio of peak flow velocity of atrial filling wave to peak flow velocity of early filling wave (A/E) were significantly greater in diabetic patients than in age- and sex-matched control subjects. Diabetic patients with retinopathy had significantly greater isovolumic relaxation time and A/E values than those without retinopathy. A/E was significantly decreased 1 month after insulin treatment in those without, but not with retinopathy. It is concluded that LV diastolic filling is impaired in mildly hyperglycemic patients with non-insulin-dependent diabetes mellitus without severe complications, the abnormality being more intense in patients with retinopathy. A short-term glycemic control results in a marked decrease in abnormalities in patients without, but not with retinopathy.