11pt, fleqn, a4paper, ]LegrandOrangeBook Background: Early catheter ablation for atrial fibrillation (AF) improves outcomes, but the optimal timing, especially in heart failure (HF) subtypes, remains unclear. Objective: To evaluate the impact of ablation timing on outcomes in patients with HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF). Methods: We used the TriNetX database (2010–2024) to identify HF patients with AF who underwent ablation. Patients were classified as early ablation (≤1 year of first AF diagnosis) or delayed ablation (1–3 years), with propensity score matching (PSM) applied to balance the baseline characteristics. The primary outcome was AF recurrence, defined by repeat ablation, direct current cardioversion (DCCV), or antiarrhythmic drug (AAD) use after a 3-month blanking period. Secondary outcomes included stroke, hospitalization, and mortality over 5 years. Results: After PSM, delayed ablation was associated with higher AF recurrence in both HFrEF (HR 1.25, p < 0.001) and HFpEF (HR 1.27, p = 0.01), as seen in multivariate analysis. In HFrEF, delayed ablation was associated with higher incidence of re-do ablation, AAD use, and DCCV, while in HFpEF, higher recurrence with delayed ablation was associated with increased AAD use. Both cohorts had similar stroke and mortality rates between early and delayed ablation. CONCLUSIONS: Delayed ablation in HFrEF and HFpEF was linked to higher AF recurrence, driven by increased redo ablations, DCCV, AAD use in HFrEF, and higher AAD use in HFpEF. Stroke and mortality rates were similar, suggesting earlier ablation may enhance rhythm control without affecting long-term survival. Condensed Abstract Delayed atrial fibrillation (AF) ablation was associated with higher (AF) recurrence in both HFrEF and HFpEF. In HFrEF, delayed ablation led to increased use of re-do ablation, cardioversion and antiarrhythmic drugs (AADs). In HFpEF, only AAD use was significantly higher with delayed ablation. Stroke and mortality rates were similar between early and delayed ablation groups.