Introduction: The interatrial septum (fossa ovalis and its muscular limbus), has been known as one of important structures to perpetuate atrial fibrillation (AF) and also known to harbor triggers initiated AF. As one of non-pulmonary vein (PV) focus, the interatrial septum was significantly related to a frequent recurrence of AF after PV isolation. Recently, we demonstrated that complex fractionated atrial electrograms were predominantly located at the left interatrial septum, which mainly due to multiple, discrete potentials from the septal bundle (SB). However, the efficacy and safety of the left SB potential guided linear ablation has not been systemically evaluated. Hypothesis: We assess the hypothesis that left septal bundle ablation has incremental value in catheter ablation for paroxysmal and persistent AF. Methods: 22 patients with symptomatic paroxysmal AF (PAF, 51짹12 years old, M:F=20:2) who underwent elimination of SB potentials combined with circumferential PV ablation (CPVA) were compared with a CPVA alone group (n=77, 53짹11 years old, M:F=65:12). 13 patients with persistent AF (PeAF, 58짹7 years old, M:F=12:1) who underwent SB ablation in addition to left atrium (LA) linear ablation with CPVA were compared to those with LA linear ablation with CPVA alone (n=30, 58짹10 years old, M:F=26:4). Results: During the 3-12 months after the ablation, all patients with PAF from the SB ablation group and 70/77 (90.9%) from patients with PAF without SB ablation were free from AF (p=0.343), while those taking anti-arrhythmic drugs were 36.4% and 17.4% in each group, respectively. AF and atrial flutter (AFL)-free rate in patients with PeAF with SB abation (84.6%) was higher than those without SB ablation (56.7%, p=0.096). Conclusions: In patients with PAF, SB ablation combined with CPVA, is feasible, safe, and has comparable efficacy to that of CPVA alone. In patients with PeAF, SB ablation led to a higher success than those with only CPVA and LA ablation.