To investigate the effectiveness and safety of low-dose sotalol (a class III antiarrhythmic beta-blocking agent) in the prevention of supraventricular tachyarrhythmias (SVTs) and to identify predictors for the occurrence of these arrhythmias shortly after coronary artery bypass grafting, 300 consecutive patients were randomized in a double-blind, placebo-controlled fashion. Patients with severely depressed left ventricular function or other contraindications for beta blockers were excluded. Beginning at 4 hours and up to the sixth day after surgery, 150 patients received 40 mg of sotalol every 6 hours. SVT was observed in 24 (16%) of 150 low-dose sotalol-and in 49 (33%) of 150 placebo-treated patients [p less than 0.005]. In patients receiving sotalol, atrial fibrillation was the only noted tachyarrhythmia, whereas in the placebo group, 42 (28%) patients had atrial fibrillation, 3 (2%) atrial flutter, 1 (0.7%) atrial tachycardia and 3 (2%) sinus tachycardia. Drug-related adverse effects necessitating discontinuation of the drug were noted in only 2 (1%) sotalol-treated patients and 4 (3%) placebo-treated patients (p = not significant). For both groups, univariate analysis indicated that older age, 1- or 2-vessel coronary artery disease, long bypass (greater than or equal to 150 minutes) and aorta cross-clamp time (greater than or equal to 120 minutes) were predictive variables for the occurrence of SVTs. Multivariate analysis showed that male sex (odds ratio 2.3), 1- or 2-vessel coronary artery disease (odds ratio 2.0) and older age (odds ratio 1.1) were independent risk factors for increased occurrence of postoperative SVT.(ABSTRACT TRUNCATED AT 250 WORDS)