BACKGROUND Complex Fractionated Atrial Electrogram (CFAE) guided ablation strategy has been widely used as one of substrate modification in patients with non-paroxysmal atrial fibrillation (AF). We questioned whether the CFAEs can recur at the same site as in de novo ablation and relate to the recurrence of AF or atrial tachycardia in patients underwent redo catheter ablation of AF. METHODS Out of 190 patients undergoing redo catheter ablation of AF, 7 patients (3.7%, 60 짹 12 years, 5 males) in whom automated 3 dimensional CFAE (NavX map) guided left and right atrial ablation was performed at the first and redo session were studied. The characteristics of CFAE were assessed by their distribution, the % area CFAE, and mean CFAE cycle length (CL). RESULTS Mean time interval to redo ablation was 21짹11 months. Recurred arrhythmia type was AF in 4, atrial tachycardia in 2, and both in 1. In 4 of 7 patients (57.1%), no PV reconnection was observed at redo procedure. In 6 of 7 patients, LA septum and anterior wall near the LA appendage (LAA) were the most common recurrence sites of CFAE. In 4 patients, AF terminated at those sites during redo ablation. In all cases, the CFAE CL was longer (62.5짹10.7ms vs. 88.9짹30.7ms, P=0.06) and % of area of CFAE smaller (29.2짹10.9% vs. 6.2짹9.1%, P=0.001) than in those at the first ablation. In 4 patients, CFAE area nearly disappeared at redo ablation procedure. There were no significant differences in LA diameter, LA volume and left ventricular ejection fraction (46.1짹8.8mm vs 41.9짹8.9mm, P=0.39, 144 짹 57.6 cm3 vs 121짹 47.2 cm3, P=0.32, 57.6짹3.7 % vs 50.9짹2.1 %, P=0.86, respectively) between those underwent first and redo ablation procedure. CONCLUSIONS The CFAEs at the septum and peri-LAA were frequently recurred, in which AF terminated during redo ablation in 4 patients. But the % of area of CFAE was smaller and mean CFAE CL was longer than in those at first ablation.