 Argon beam coagulator is one of the most common hemostasis tools in heart surgery. It can also cause coagulation necrosis of the myocardium and do not do harm to the nearly myocardium the same as bipolar radiofrequency ablation. In the investigators early study the investigators use the coagulation de plasma argon to burn the endocardium. And in the investigators 6 mouth follow up, the rate of cardioversion is 90. In this study the investigators plan to use argon beam coagulator to ablate these gaps. 