Background: Atrial tachycardias (ATs) developed following atrial fibrillation (AF) ablation are known to be caused by recovered pulmonary vein (PV) conduction or reentry at incomplete ablation lines. However, it remains unclear whether ATs developed after AF termination during ablation guided by complex fractionated atrial electrograms (CFAEs) are related to incomplete ablation or caused by proarrhythmic effect at the sites of CFAEs. We investigated the relationship between the sites of CFAEs and the foci of these secondary AT. Methods: The sites of CFAEs were assessed using 3-D automated map (NavX) in twenty persistent AF (PeAF) patients (mean age 59.4짹11.0 years old, 16 males, mean LA size 44.3짹5.3 mm) showing AT during catheter ablation including circumferential PV isolation and ablation at CFAEs. Results: Among 20 patients, AT developed following organization of AF during ablation in 9 patients (group 1), and in 11 patients, AT induced by right atrial pacing after AF ablation (group 2). AT were macroreentrant in 18 patients and focal in 2 patients. The sites of AT termination (5 in perimital isthmus, 5 in carvo-tricuspid isthmus (CTI), 3 in left atrium (LA), 3 in septum, and 4 in right atrium (RA)) were matched with one of the CFAE areas in 10 patients (50%, 6 in group 1 vs. 4 in group 2), while the others (n=10) were not matched. In 15 patients (75%), sites of AT termination were in these CFAEs site and CTI. During the mean 12.7짹10.6 months, recurrence of sustained arrhythmia was observed in 20% (AT in 1 and AF in 3). Sinus rhythm was maintained in 85% including a second session (n=1). Conclusion: This study demonstrates that automated map of CFAEs-targeted ablation in addition to CTI block is effective in substantial number of the patients with AT developed following PeAF ablation.