Atrial fibrillation (AF) is now recognized to be main antiarrhythmia target in the new millennium as it increases morbidity and mortality in prevalence with age. Based on the current knowledge, the hope to cure AF is on nonpharmacologic approaches whose advantage is limited in the therapy of chronic sustained AF, the most common clinical arrhythmia, by the fact that the number of patients treated by Maze procedure has been small in spite of its very high clinical success rate, and that the low success rate and high recurrent rate of catheter ablation in mimicking Maze procedure. So the nonparmacologic 4 approaches of chronic AF is in the bud. This study is to locate the points critical to the maintain of AF and to simply the catheter ablation procedure in cure of AF according to the anatomic and electrophysiological property of the atriums in dogs. The electrophysiological property and the effects on the induction and maintain of AF of the connections of two atriums before and after they were blocked were evaluated and compared to try to find out the role of them in the initiation and maintenance of AF under epicardial and endocardial mapping technique. The Bachmann抯 bundles and coronary sinus musculatures were blocked by epicardial and endocardial radiofrequency ablation and the the conductive time(CT)and effective refractory period(ERP)were measured before and after the ablation under direct vision. In acute AF models induced by burst stimuli and acetyl- P -methylcholine, the AF thresholds and maintaining time before and after the ablation were measured and compared, and then under biatrial pacing the procedures above were repeated again. The results showed that the partly blockage of the connections of two atriums made little effect on the induction and maintenance of AF. The completely blockage made the CT between two atriums longer, and the threshold of induced A.F lower, and the time for ALF maintaining shorter significantly. Biatrial pacing made the activation time of total atrium shorter than that in sinus rhythm, and the AF threshold high, but no effect on the maintenance of AF. In conclude, blockage of the connections of atriums made the S maintaining time of induced AF shorter in this kind of canine models. The study indicated that the connections of two atriums might play a role in the mechanism of AF maintenance.