Abstract： Background Pulmonary-vein isolation (PVI) is currently used for the treatment of chronic and paroxysmal atrial fibrillation and a major risk of PVI is thromboembolism. The purpose of this study was to observe embolic event rate in patients with persistent or paroxysmal atrial fibrillation (AF) undergone PVI.Methods Circumferential PVI (CPVI) was performed in 64 consecutive patients with persistent AF (42 men, aged (60.0±9.1) years) and in 84 consecutive patients with paroxysmal AF (53 men, aged (61.4±9.3) years). Warfarin was administrated in all patients before ablation for at least 3 weeks ((5.2±2.6) weeks) and continued for at least 3 months post ablation with international normalized ratio (INR) of 2.0-3.0. During CPVI, intravenous heparin was given at a dose of 5000-8000 U or 75-100 U/kg, followed by 1000 U or 12 U/kg per hour.Results In patients with persistent AF, 1 patient developed embolic event during ablation and 3 patients developed embolic events after ablation. In contrast, no thromboembolic event was observed in patients with paroxysmal AF (4/64vs 0/84, P=0. 033).Conclusion Thromboembolic event rate related to CPVI is significantly higher in patients with persistent AF than that in patients with paroxysmal AF.