- Fourteen morbidly obese patients scheduled for gastric bypass surgery were diagnosed preoperatively as suffering from sleep apnea syndrome. There were 13 males and 1 female aged 24 to 59 years. Mean preoperative excessive body weight was 222 +/- 38%; mean apnea index prior to surgery was 84 +/- 44. A whole night lead II ECG tracing was performed as part of the polyhypnographic recordings and was evaluated for cardiac arrhythmias. Studies were performed in all patients preoperatively and 6 months thereafter. Statistical analysis was done using the Student's paired t-test. In this group a high incidence of atrial and ventricular arrhythmias was found. Marked sinus arrhythmia was encountered in all patients and extreme sinus bradycardia in 4 of them. In a consecutive sleep study performed 6 months postoperatively most cardiac arrhythmias disappeared. Marked sinus arrhythmia persisted in only two patients and severe ventricular premature beats (Lown's grade III-IV), found preoperatively in all patients, were still present postoperatively in only two, although in a much milder form. Surgical weight reduction, therefore, is a valuable method in the abolishment of life-threatening cardiac arrhythmias of the morbidly obese sleep-apneic patient.