A total of 116 patients undergoing coronary revascularization were randomized preoperatively in a double-blind manner to receive 80 mg daily of propranolol or placebo in the postoperative period. Preoperatively, all patients had been receiving at least 80 mg of propranolol a day to the time of the operation. In addition, all patients had a left ventricular ejection fraction of 0.4 or more, no history of supraventricular tachyarrhythmia (SVT), and no need of digitalis preparations or other antiarrhythmic drugs. All patients were monitored for 5 days and propranolol or placebo was started 24 hours postoperatively. SVT was documented with biatrial electrograms in all cases. Study groups were similar in postoperative creatine kinase MB levels and postoperative weight gain, but the placebo group tended to be older and have more grafts per patient. Seven patients randomized were dropped from the study, two with perioperative infarction, four with persistent ventricular arrhythmias necessitating quinidine or procainamide, and one with persistent postoperative hypotension (placebo). There were no significant differences in the incidence of postoperative SVT in these two groups: 13.2% in the propranolol group and 16.1% in the placebo group. We conclude that 80 mg daily of propranolol given postoperatively to patients undergoing coronary revascularization does not effectively reduce the incidence of SVT.