Background Radiofrequency catheter ablation (RFCA) by either segmental or circumferential pulmonary veins (PVs) isolation (PVI) from the left atrium (LA) has resulted in cure of atrial fibrillation (AF) in 50% to 80% of patients. However, AF recurrences after initial PVI are not uncommon, and multiple sessions are required to achieve better clinical outcome. This study evaluated the electrophysiological characteristics of patients with recurrent AF after initially successful PVI and the final outcome after repeat procedure. Methods and Results Among 114 patients (54짹13 years old) with paroxysmal (PAF, n=85) and persistent (PeAF, n=29) AF underwent PVI, 25 patients (22%, 51짹11 years, 17 PAF/8 PeAF) with recurrent AF returned for repeat mapping and ablation 193짹237 days (1-820 days) after the first PVI. RFCA was done with 5-mm tip catheter with a target temperature of 53-55째C and a maximum power output of 30 to 50 watt for 40 to 60 sec. To determine return of conduction of previously isolated PV. a circular mapping catheter (n=20) or noncontact mapping system (EnSite 3000, n=5) was used. Ectopy was provoked with isoproterenol (up to 10 mg/min), burst pacing, and post-DC cardioversion immediate reinitiation of AF. 46 previously isolated PVs (46/55, 83.6%) had evidence of recovered PV conduction. The ectopies triggered AF originated from previously targeted PVs (13/25, 52%) and non-PV foci (4/25, 16%). Over a period of 21짹16 months, 22 patients (88%, 16/17 PAF, 6/8 PeAF) were clinically improved by repeat PVI and non-PV foci elimination. Conclusions Most recurrent AFs after PVI are caused by reconduction of previously isolated PVs. The recurrent triggers originated from non-PV foci were not uncommon (16%). Repeat PVI and identification of non-PV foci provides significant clinical benefit and may enhance long-term efficacy.