OBJECTIVE: Weight loss improves cardiac abnormalities associated with severe obesity. We evaluated the impact of weight loss following laparoscopic gastric bypass (LGBP) on left ventricular (LV) geometry and function in obese patients. METHODS: Twenty-six patients with severe obesity (41 ± 8 years, 50% women) underwent Doppler echocardiograms before and after LGBP, to measure LV geometry, excess of LV mass relative to hemodynamic load and systolic and diastolic function. RESULTS: Pre-operatively, 85% of patients exhibited LVH, and 62% hypertension and metabolic syndrome, reflecting high cardiometabolic risk. After 8 ± 4 months of follow-up, the average weight loss was 19 ± 8%. Weight loss was significantly associated with improved metabolic parameters and reduced heart rate (-9 bpm), systolic (-11 mmHg) and diastolic (-6 mmHg) blood pressure (all p < 0.02). After surgery, there was significant reduction in relative wall thickness (0.43 ± 0.07 versus 0.39 ± 0.06), LV mass index (63 ± 14 g/m(2.7) versus 49 ± 10 g/m(2.7)) and excess of LV mass in relation to hemodynamic load (all p < 0.004). LVH remained in 54% of patients, hypertension in 23% and metabolic syndrome in 27%. Ejection fraction and Doppler indices of diastolic function did not change significantly, even after adjusting for changes in heart rate. All favorable changes in LV geometry and function were also confirmed in the subgroup with <9 month follow-up (median), whereas no further improvement could be detected in patients with longer follow-up. CONCLUSIONS: In patient with severe obesity, LV geometry and systolic function improved rapidly after LGBP, without evidence of further improvement during prolonged follow-up.