In order to evaluate the left ventricular (LV) response to isometric exercise in diabetics, 15 young insulin-dependent diabetic subjects and 12 control subjects of similar age and sex distribution performed a handgrip test during echocardiography. No base-line differences in hemodynamic or echocardiographic parameters were found between diabetic and control subjects. The heart rate and blood pressure responses to handgrip exercise were similar in the two groups, and LV dimensions, shortening fraction and velocity of circumferential fiber shortening remained unchanged in both groups. Three diabetic subjects had an impaired LV functional response to handgrip (a decrease of more than 5 percentage units in the shortening fraction). These 3 patients had high HbA1 values (17.6-18.2%) and modest correlations existed between decrease in the shortening fraction during handgrip and concentrations of HbA1 (r = 0.70, p less than 0.01) and fasting blood glucose (r = 0.62, p less than 0.01). Thus, most young insulin-dependent diabetic subjects appear to have a normal LV response to isometric exercise, but poor blood glucose control seems to be accompanied by a slight impairment of LV functional reserve.