A 7-month-old girl weighing 5.3 kg, presented with atrial septal defect (ASD) and paroximal supraventricular tachycardia (PSVT). The preoperative electrophysiological study could not be performed because of the severe heart failure. On suspicion of a concealed Wolff-Parkinson-White (WPW) syndrome, whose accessory pathways conduct in the retrograde direction only, the operation was performed. The intraoperative epicardial and endocardial mappings revealed the presence of a left-posterior retrograde accessory pathway. This accessory pathway was successfully ablated by a cryoablation using transseptal superior approach. The postoperative course was uneventful without a permanent heart block. We report a successful surgical repair for an infant with concealed WPW syndrome, who revealed severe heart failure because of PSVT and ASD.