['To assess long-term changes in left atrial (LA) volume in patients with morbid obesity [body mass index (BMI) >or=35 kg/m(2) with co-morbidities] and extreme obesity (BMI >or=40 kg/m(2)), after surgically-induced weight loss (WL) after gastric bypass surgery.', 'We reviewed 57 patients who underwent gastric bypass surgery and had echocardiograms both before and after the operation. A control group was frequency-matched for BMI, sex, age, and for duration of follow-up. After a mean follow-up of 3.6 years, LA volume did not change significantly in patients who underwent bariatric surgery, but increased in the control group by 15 +/- 28 ml (P < 0.0001), and 0.1 +/- 0.2 ml (P < 0.0001) for height-indexed LA volume, with a difference between cases and controls that remained significant after adjusting for potential confounders (P = 0.01). In the study population as a whole, there was a positive correlation between change in body weight and change in LA volume (r = 0.22, P = 0.006) independent of clinical conditions associated with LA enlargement.'] Does major weight loss prevent long-term left atrial enlargement in patients with morbid and extreme obesity?