Atrial tachycardia (AT) is recognized as a risk factor of sudden death (SD) in patients with transposition of the great arteries (TGA) after atrial switch operation. A 20-year-old man with TGA who had undergone a Senning operation experienced a near-miss SD event 1 day after appearance of AT. He was successfully resuscitated by electrical defibrillation for documented ventricular fibrillation. An electrophysiological study showed three types of AT, and all of them were terminated by radiofrequency catheter ablation (RFCA). We consider that symptomatic AT against cardiac medications is indicated for RFCA therapy.