Six patients underwent cardiac surgery for refractory tachyarrhythmias. Four had Wolff-Parkinson-White syndrome and 2 ventricular tachycardias after myocardial infarction. The results of preoperative electrophysiologic studies corresponded in 5 cases to intraoperative findings of epicardial and pace-mapping. These patients were free of symptoms for the 4-16 months' follow-up. In one patient with divergent results, tachycardia and preexcitation returned two months postoperatively. In the light of the foregoing the authors suggest surgical treatment for 1. preexcitation with life-threatening arrhythmias, 2. refractory ventricular tachycardias with coronary artery disease and 3. preexcitation in patients undergoing open heart surgery for other reasons.