Introduction: Cardiac tamponade (CT) is known as one of frequent and major complications after radiofrequency catheter ablation (RFCA) of atrial fibrillation (AF). We retrospectively evaluated the procedural characteristics, treatment and clinical outcome of the patients with CT. Methods: Procedural characteristics of all cases with CT which developed during AF ablation were assessed. The safety and long-term outcome of continuing RFCA for AF in whom CT developed before achieving end points of ablation were investigated. Results: 1) The incidence of CT was 3.6% (41 among 1137 cases). 41 patients with CT were 58.2짹9.2 years old and 30 patients had paroxysmal AF. All patients had CHADS2 score 0 or 1 except 3 patients and 16 patients (39%) continued to take warfarin immediately before RFCA. 2) 5 cases of CT developed during acquisition of 3-D geometry of the left atrium (LA), 32 cases developed during RF ablation and 4 cases were found within 3 days after RFCA. 3) Most patients except 4 patients were treated successfully by pericardiocentesis and then underwent further ablation after hemodynamically stabilized and confirmed bleeding stopped. Peak impedance during RF was 145.5짹41.6 Ohm under peak power 28.6짹13.5 Watt. ACT level just before CT was 384.2짹151.7 s and decreased to 275.9짹77.7 s after reversal with mean 36.2짹17.9 mg of protamine sulfate at the time of continuing RFCA. Suspected perforation site were right-sided pulmonary veins (PVs) in 13 cases, left-sided PVs in 7 cases, LA roof in 2 cases and the right atrium in 6 cases. 4) 4 patients underwent emergency operation due to hemodynamic instability and massive pericardial blood refractory to closed pericardiocentesis. Perforation sites revealed during operation were the junction between right superior PV and LA in 2 patients, 1 in the LA roof, and 1 great cardiac vein. 5) The recurrence of AF or atrial tachycardia (AT) after RFCA was higher (42.5%, 17/40) in patients with CT than in those without CT (20.9%, 84/402, p<0.01). Conclusions: Significant cases of CT developed during catheter manipulation of mapping catheter inside the LA or ablation of the LA roof, especially at the junction with right superior PV. Most patients could be treated by pericardiocentesis and continued further ablation to achieve end points, but had higher rate of recurrence of AF/AT during follow up of 22.4짹15.1 months.