Roof-dependent atrial flutter (AFL) is a major tachyarrhythmia rotating in the left atrium (LA). Here, we describe a case of roof-dependent AFL during atrial fibrillation ablation. LA posterior wall (LAPW) debulking ablation was performed before the induction. Atrial tachycardia (AT) was induced by burst pacing, and the 3D mappings showed a focal pattern from the LA inferior area. The post-pacing interval from the roof and bottom line corresponded to the AT cycle length. The LAPW debulking ablation masked roof-dependent AFL due to the lack of endocardium potentials in the LAPW. We report that roof-dependent AFL connected by epicardium fibers.