Twenty-one patients were successfully resuscitated from cardiac arrest. Electrocardiograms (ECG) during cardiac arrest were recorded in 14 patients with ventricular fibrillation in 7, ventricular tachycardia in 4, cardiac standstill in three, Torsade de Points in one and atrial fibrillation with rapid ventricular response in 1. Thirteen patients (group I) had structural heart disease or primary ECG abnormality and 8 patients (group II) had no apparent heart disease. Electrophysiologic study (EPS) was performed in 12 patients of group I and 5 of group II. In group I, ventricular tachycardia was induced in 7, and His-ventricular conduction disturbance was demonstrated in 2, and 2 patients with Wolff-Parkinson-White (WPW) syndrome had an effective refractory period of the antegrade accessory pathway <250 msec. No patients in group II showed abnormal EPS findings. Spasm provocation test was performed in 8 patients (2 in group I and 6 in group II). Coronary spasm was induced In 5 patients (1 in group I and 4 in group II). Two patients in group 11 had positive results of upright-tilt testing. During the follow-up period, 2 patients died suddenly in group I and 1 patient whose cause of cardiac arrest was unknown had a recurrence of cardiac arrest. In group II, all patients whose etiology could be demonstrated by serial examinations had good prognosis. In conclusion. EPS is useful in evaluation of the cause of cardiac arrest especially when patients have structural heart disease, and coronary spasm may be involved in patients with cardiac arrest without apparent heart disease.