This report describes the histopathological findings following successful RF isthmus ablation for common atrial flutter in a 68-years-old man using a long 8-mm tip ablation catheter. No acute complication was observed. The patient died 3 weeks after ablation due to severe heart failure and consecutive pneumonia. Lesion width (1.0 and 2.4 cm) and depth (0.4 and 0.8 cm) was measured. The right coronary artery showed an intramural hemorrhage adjacent to the side of the lesion. However, despite this finding no apparent injury of other layers of the coronary artery was detectable.