 The objective of the study is to make up the technique blind spots of the bipolar radiofrequency ablation in the surgical treatment of atrial fibrillation with rheumatic heart disease by using argon beam coagulator. And to improve the rates of cardioversion of atrial fibrillation after surgery, to decrease the long-term recurrence rate of atrial fibrillation and to compare the early term and long term outcomes of bipolar radiofrequency ablation and bipolar radiofrequency plusargon beam coagulator ablation. 