Electrophysiologic events in a 52-year-old man with Wolff-Parkinson-White (W-P-W) syndrome, type B, recurrent supraventricular tachycardias, and coronary artery disease were studied during cardiac catheterization and at open-heart surgery.During cardiac catheterization reciprocal tachycardias were repeatedly initiated by premature atrial beats and terminated by rapid right atrial pacing. Our results confirm that the tachycardia usually seen in the W-P-W syndrome is reciprocal tachycardias with orthograde conduction to the ventricles through the normal atrioventricular conduction system and retrograde conduction to the atria via the Kent bundle.The epicardial surface of the ventricles was “mapped’ at surgery. The earliest site of excitation was the posterior base of the left ventricle near the crux of the heart. Kent bundle conduction was temporarily ablated with lidocaine (Xylocaine) hydrochloride.This is the first case of W-P-W syndrome, type B, in which the anomalous A-V bundle entered the left ventricle. Our results indicate that the analysis of the electrocardiogram in localizing an abnormal A-V connection cannot be relied upon completely.