To determine if the prophylactic administration of oral verapamil is effective in reducing the incidence of supraventricular tachycardia after myocardial revascularization, 141 patients were entered into a double-blind randomized trial. Seventy patients received verapamil 80 mg every 8 hours beginning immediately after operation and continuing for 5 days, and 71 patients received placebo. Patients were monitored during the study period and observed for the occurrence of supraventricular tachycardia. The verapamil and placebo groups were similar with regard to sex, age, preoperative antianginal drugs, number of bypass grafts, average bypass time, and average occlusion time. A total of 39 patients had supraventricular tachycardia, 20 were receiving verapamil, and 19 were receiving placebo. The average ventricular rate was 127 +/- 13 beats/min for the verapamil group with supraventricular tachycardia compared with 140 +/- 12 beats/min for the placebo group with the mean differences not significant (p = 0.10). On the basis of these data, it is concluded that verapamil 80 mg every 8 hours beginning early after myocardial revascularization is not effective in reducing the incidence of supraventricular tachycardia.