To determine if uncomplicated obesity is associated with systolic dysfunction or impairment of left ventricular (LV) filling, 40 normotensive, white, asymptomatic, obese subjects (16 men and 24 women, mean +/- SD age 35 +/- 13 years; body mass index 36 +/- 6 kg/m(2)) and 40 normotensive, normal-weight, white volunteers matched for age and sex distribution, were studied Doppler echocardiography. Endocardial and shortening did not show differences between groups (obese = 33 +/- 4% and 17 +/- 2%; normal weight = 33 +/- 3% and 18 +/- 2%, respectively). LV mass index was higher in obese than in normal-weight subjects (p <0.0001). Obese persons had prolonged isovolumic relaxation time (p <0.0001), lower transmitral peak early diastolic filling wave (E) velocity (p <0.02), higher E velocity deceleration time (p <0.002), and lower E/atrial diastolic filling wave (A) flow velocity ratio (p <0.01) than did normal-weight subjects, even after controlling for age and blood pressure. Between-group differences in E and E velocity deceleration time disappeared when controlling for LV mass index, whereas prolonged isovolumic relaxation time in obesity was independent of LV mass, chamber dimension, and end-systolic stress. LV filling variables were not statistically related to endocardial or midwall shortening, both as absolute value or as a percentage of that predicted from wall stress. We conclude that uncomplicated obesity is associated with primary impairment of LV isovolumic relaxation; abnormalities of early passive filling flow in obesity are associated with increased LV mass.