Background. This study tests the hypothesis that post-cardioplegia electrophysiologic recovery is influenced by the duration of cardioplegic arrest. Methods. Pigs were randomized to various durations of cardioplegic arrest (group I, 15 minutes; group II, 60 minutes; group III, 120 minutes). Electrophysiologic data included limb lead, atrial and ventricular epicardial, and ventricular endocardial electrocardiograms. Variables included times for earliest electrical activity and sinus rhythm; number of defibrillations; mechanism for reperfusion ventricular fibrillation; and time until last ventricular fibrillation. Results. Time to last ventricular fibrillation was 73 ± 8, 134 ± 23, and 238 ± 23 seconds for groups I, II, and III (mean ± standard error of the mean; p < 0.05 between group III versus groups I and II). The number of defi-brillations was 1.0 ± 0.3, 5.8 ± 1.2, and 10.5 ± 1.1 for groups I, II, and III (p < 0.05 between groups). The time to sinus rhythm was 66 ± 8, 192 ± 27, and 249 ± 23 seconds for groups I, II, and III (p < 0.05 group I versus groups II and III). The most common mechanism for reperfusion arrhythmias was an accelerating ventricular tachycardia that initiated fibrillation (79 of 167 episodes). However, in many instances postdefibrillation amplifier saturation masked the initiation of reperfusion arrhythmias. Conclusions. Electrophysiologic recovery after cardioplegic arrest is influenced by the duration of cardioplegic arrest. © 1998 by The Society of Thoracic Surgeons.