Cardiac structure and systolic as well as diastolic functions were evaluated by 2-dimensional M-mode echocardiography in lean and obese patients who were either hypertensive or normotensive. Diastolic function, as assessed by diminished normalized early peak filling rate and prolonged duration of rapid filling, was decreased in hypertensive patients compared with normotensive patients (p = 0.02). When compared with lean patients with similar blood pressure levels, obese patients exhibited a lower normalized peak filling rate (p = 0.0014) but no difference in duration of rapid filling. A significant correlation was observed between the normalized peak filling rate and either body mass index or left ventricular (LV) mass (r = 0.355 and r = -0.32, respectively; p less than 0.001). Obese patients had greater LV end-diastolic and systolic dimensions (p less than 0.005 and p less than 0.02, respectively), LV wall thickness (p less than 0.05) and LV mass (p less than 0.007) than lean patients. Impairment of LV filling was most pronounced in obese hypertensive patients. It is concluded that the burden on the left ventricle imposed by obesity causes cardiac enlargement and impairment of LV filling regardless of levels of arterial pressure.