BACKGROUND: Regional differences in optimal contact force (CF) to prevent acute pulmonary vein reconnection (APVR) during catheter ablation for atrial fibrillation (AF) remain unclear. OBJECTIVE: The purpose of this study was to evaluate regional difference in optimal CF during AF ablation. METHODS: This single-center observational study evaluated data from 57 consecutive drug-refractory AF patients (mean age, 62 ± 11 years; 43 males) who underwent initial pulmonary vein isolation (PVI) using the THERMOCOOL® SMARTTOUCH™ (Biosense Webster, Diamond Bar, CA, USA) catheter from June to August 2013. APVR was defined as the time-dependent reconnection >20 minutes after initial PVI and/or reconnection evoked by intravenous adenosine administration (20 mg). Point-by-point relationships between the reconnected points and their CF values were evaluated. RESULTS: Total 72 gaps causing APVR were observed. Of a total of 4,421 ablation points, 285 (6.4%) were associated with APVR. The average CF value of the points with APVR was significantly lower than that of those without (APVR vs. no APVR; 7.5 ± 6.7 g vs. 9.9 ± 8.4 g; P < 0.0001). The areas under the curve and optimal CF values differed between segments (range 0.593-0.761 and 10-22 g, respectively). The optimal CF value was highest in bottom of the right PV and posterosuperior right PV segments (22 g) and lowest in posteroinferior right PV segment (10 g). CONCLUSIONS: There was a regional difference in optimal CF values to prevent APVR, and the optimal CF value to prevent APVR with >95% probability was 10-22 g, depending on the individual peri-PV segments.