Ablation of persistent atrial fibrillation is still a challenge for the ablationist. Extensive ablation is required under some conditions and could lead to some unintended complications. Here we report a case of atrium-atrioventricular node block complicating multiple catheter ablation procedures for persistent atrial fibrillation. After extensive ablation, including circumferential pulmonary vein ablation, linear ablation at the left atrial roof, mitral isthmus, atrial septum, cavotricuspid isthmus, and complex fractionated atrial electrogram ablation, conduction obstacle was found, and sinus impulse could not travel from the right atrium, atrial septum and left atrium to atrioventricular node. The case indicated that intensive ablation at some key sites, especially the interatrial septum, should be careful during ablation of atrial fibrillation.