BACKGROUND Obesity causes structural changes to the heart that may influence its function. Furthermore, morbid obesity is associated with an acquired prolongation of the QTc interval that may lead to potentially hazardous arrhythmias. The present study investigated the effect of body weight loss following vertical banded gastroplasty (VBG) on the QTc interval. METHODS 17 morbidly obese patients, scheduled for elective VBG, were studied before the operation and 8-10 months postoperatively, when each patient had achieved a weight loss of >/= 25% of the preoperative body weight. RESULTS 15 patients achieved significant body weight loss of >/= 25% within the first 8-10 postoperative months (P <0.001). This weight loss, corresponding to an excess weight loss of 48.7% and a mean body mass index (BMI) reduction from 49.7 kg/m2 to 36.6 kg/m2, was followed by significant shortening of the QTc interval from 428 msec to 393 msec (P <0.001). CONCLUSIONS The significant postoperative weight loss following VBG was accompanied by shortening of the QTc interval. This effect is expected to reduce the incidence of fatal conditions associated with the long QT syndrome, such as malignant ventricular arrhythmias and sudden death, and therefore improve morbidity and mortality.