Background: Catheter ablation of atrial fibrillation has evolved from ablation of arrhythmogenic foci within the pulmonary veins (PV) to complete electrical isolation of the PV, often guided by perimetric mapping with a multi-polar loop catheter positioned at the rim of each of the PV ostia. However, incomplete linear lesions may form the milieu for subsequent macroreentrant tachycardias, which are usually persistent and which may be poorly tolerated and thus more symptomatic than the original AF. In this respect, the ���mitral isthmus,��� defined as the narrow region spanning the mitral annulus to the ostium of the left inferior PV, has been promising, the improved success rate for cure of AF was achieved at the cost of a slightly higher risk of complications. However, mitral isthmus have not been fully evaluated. Methods: We evaluated pulmonary vein anatomy and mitral isthmus of atrial fibrillation patients (AF group; n=43) by a 64- slice multidector computed tomography (MDCT) including virtual endoscopic view. Age-, sex matched normal control persons without history of AF (control group; n=43) compared with AF group. Mitral isthmus was defined as the area from left inferior PV to mitral annulus. Conclusion: Mitral isthmus was more longer in AF patients and the longer isthmus had more complex morphology. Because It was harder to draw a line over the complex anatomy of isthmus, pre-evaluation of mitral isthmus by MDCT may be useful in AF treatment with catheter ablation