Background : Mitral isthmus dependent atrial tachycardia commonly developed during catheter ablation of atrial fibrillation. Mitral isthmus line was performed in many centers, but the success rate was low. We performed anterior line connecting roof line and anterior mitral annulus as alternative methods. We had tried to achieve complete block of distal Bachmann bundle along the medial side of left atrial appendage to treat atrial tachycardia and there was a safety concern about blockage of natural biatrial electrical conduction. AIMS : To assess the effects of bachmann bundle block on the left atrial and ventricular function. Methods : We measured and compared echocardiographic parameters in patients with Bachmann bundle block (n=20) and without block (n=27) 3 months after catheter ablation. Complete Bachmann block was comfirmed by differential pacing during index procedure. Results : All the study population (n=47) was diagnosed as persistent atrial fibrillation and sinus rhtythm was maintained on one antiarrhythmic agent drug during 3 months follow-up period. There were no differences in diastolic and systolic function in echocardiographic parameters. Echocardiographic results were shown in Table. Conclusion : Catheter ablation of anterior wall can be safely performed in mitral isthmus dependent atrial tachycardia and complete Bachmann bundle block has no adverse effects on left atrial and ventricular function.