The success of methods that ablate atrioventricular (AV) node reentry demonstrates that extranodal tissue is part of the reentry circuit. The hypothesis of this study is that atrial tissue approaching the posterior AV node is part of the AV node reentry circuit and is especially suitable for complete division with sparing of AV conduction. This study measured AV node function after either an anterior or posterior perinodal incision. The only significant change noted in antegrade function was a lengthening of the Wenckebach point after the posterior incision. Retrograde AV conduction and ventricular echoes were abolished by the posterior incision, whereas the anterior incision had no discernible effect on retrograde AV node function. Anatomic analysis of the two incisions showed that the posterior incision completely interrupted the posterior atrial input to the AV node, whereas the anterior incision spared the medial input to the AV node. The atrial tissue posterior to the AV node is anatomically suited for complete interruption. Ablation of atrial tissue posterior to the AV node to proposed for abolishing AV node reentrant tachycardia. © 1994.