The aim of this study was to examine the effect of surgical weight reduction on cardiac structure and function and to seek the determinants of these changes. Sixty-six severely obese adults (BMI >or=35 kg/m(2)) who received bariatric surgery underwent echocardiographic examination before and 3 months after surgery. At 3 months after surgery, BMI and systolic blood pressure (BP) decreased (43.3 +/- 6.3 to 34.1 +/- 5.6 kg/m(2), P < 0.001, and 146 +/- 12 to 130 +/- 14 mm Hg, P < 0.001, respectively). In left ventricular (LV) geometry, the relative wall thickness (RWT) and LV mass index decreased significantly (0.43 +/- 0.05 to 0.35 +/- 0.05, P < 0.001, and 50 +/- 11 to 39 +/- 11 g/m(2.7), P < 0.001, respectively) without changes in chamber size. Multivariate analyses showed change in systolic BP to be an independent predictor for the changes in RWT and LV mass index. In myocardial performance, peak systolic mitral annular velocity and all diastolic indexes showed significant improvements. We concluded that LV hypertrophy and function improved rapidly after bariatric surgery in severely obese adults. BP reduction was the major determinant for the regression of LV hypertrophy in the early stage of surgical weight reduction.