A 19-year-old man who underwent bicaval orthotopic heart transplantation for idiopathic dilated cardiomyopathy complained of palpitations 2 weeks after the heart transplantation. An ECG revealed paroxysmal atrial tachycardia (AT) with a cycle length of 260 ms and the P wave morphology of the AT was similar to that during sinus rhythm. Echocardiography showed normal contraction. No rejection, vasculopathy, or infection was observed. An electrophysiologic study and catheter ablation guided by a noncontact mapping system were performed due to drug refractory AT. The AT was induced spontaneously by isoproterenol infusion. The activation sequence of the AT exhibited a focal pattern, and the breakout site of the AT into the donor right atrium was just 12 mm below the breakout site of the donor sinoatrial node. Radiofrequency catheter ablation eliminated this AT and resulted in an improvement in the symptoms.