Introduction Exit block, which is difficult to strictly confirm and cannot be adopted for adenosine triphosphate (ATP) injections to provoke dormancy, is an essential concept of atrial fibrillation (AF) ablation. We investigated exit conduction using high frequency stimulation (HFS) and evaluated whether dormant “exit” conduction of the pulmonary veins (PVs) and left atrial posterior wall (LAPW) would remain in patients in which an encircling isolation of all PVs and LAPW isolation (Box PVI) were performed. Methods We enrolled 345 consecutive patients with various severities of AF undergoing a Box PVI and defined the procedure endpoint as complete bidirectional block with no dormant “entrance and exit” conduction of all PVs and the LAPW using HFS and ATP. Results Dormant “exit” conduction of the PVs with HFS delivered at the PV carina following an ATP injection remained in 0.9% after additional applications, and that for the LAPW was provoked in 5.5%, which remained in 1.4%. Our definition of a complete bidirectional Box PVI was satisfied in 79.7% and showed the best clinical outcome. In the non-paroxysmal AF group, there were significant differences in the recurrence rates between the groups with and without a complete LAPW isolation, however, the clinical outcome was independent of a complete LAPW isolation in the paroxysmal AF group. Conclusion HFS delivered at the PV carina and LAPW following a Box PVI could clearly elucidate true exit block, and a concomitant ATP injection could define dormant “exit” conduction, suggesting incomplete lesions that had been missed.