BACKGROUND Obesity frequently results in structural and physiologic changes in the cardiovascular system. Whether weight reduction leads to reversal of these changes is not well-established. This investigation sought to identify the effect of a weight reduction program on right and left ventricular structure and function. METHODS Sixty-two patients presenting to the eating disorders clinic at a single academic institution for weight loss programs were prospectively enrolled. Baseline and follow-up transthoracic echocardiograms were obtained after at least 10% weight reduction or 6 months after baseline echocardiogram. Complete 2-dimensional echocardiograms were performed with M-mode, flow Doppler, and tissue Doppler evaluation. RESULTS Patients lost an average of 28.2 +/- 3 kg over a period of 266 +/- 36 days. Left ventricular mass decreased significantly from 255.87 +/- 12 to 228 +/- 11 gm. There were no statistically significant changes in contractility or diastolic indices. The ratios of early-to-late diastolic mitral inflow velocities (E/A) increased from 1.30 +/- 0.05 to 1.32 +/- 0.06. The ratio of early mitral flow to early annular velocity (E/Em) also increased from 5.57 +/- 0.22 cm to 5.82 +/- 0.23 cm. Deceleration time increased from 213.26 +/- 5.3 s to 228.47 +/- 5.7 s. CONCLUSIONS Weight reduction is associated with decrease in left ventricular diastolic size and left ventricular mass. This weight reduction is not associated with statistically significant improvement in systolic or diastolic function.