A 59-year-old male was admitted for catheter ablation of paroxysmal supraventricular tachycardia. He had a previous history of lower-thoracic esophageal cancer treated by chemoradiation therapy 2 years earlier. The patient had received a total dose of 61 Gy and the heart had been included in the radiation therapy (RT) field. The 12-lead ECG during sinus rhythm was within normal range (Picture 1A). The 12-lead ECG during tachycardia showed long RP tachycardia (Picture 1B). The endocardial voltage map of the right atrium (RA) by electroanatomical mapping revealed a broad low voltage area including scar tissue which was suggested by non-captured, high output pacing, mainly in the free wall of the RA (Picture 2A). The activation map during the tachycardia demonstrated a focal activation pattern with the earliest activation site in the low lateral RA (Picture 2B) where the mid-diastolic potentials during the tachycardia were recorded (Picture 3), suggesting scarrelated reentry as the mechanism of the tachycardia and suc-