Abstract Funding Acknowledgements None Background Atrial fibrillation (AF) ablation has been known to contribute to a good prognosis in heart failure patients and improve their systolic function. However, the impact of the post-procedural systolic function on the prognosis in them remains unclear. Purpose To investigate the impact of the left ventricular ejection fraction (LVEF) following AF ablation in patients with systolic dysfunction. Methods Out of 1078 consecutive patients who underwent AF ablation including extensive pulmonary vein and superior vena cava isolation, 170 with an impaired pre-procedural LVEF (< 50%) were evaluated. They experienced at least one echocardiographic follow-up within one year after the index procedure. The primary outcome was the composite of all-cause death or heart failure hospitalisations (HFHs). In addition, we categorised the patients into three groups according to the post-procedural LVEF within one year to evaluate the outcome: reduced LVEF (rEF, LVEF < 40%), mid-range EF (mrEF, 40% ≤ LVEF < 50%) and preserved LVEF (pEF, LVEF > 50%). Results After the index procedure, the patients’ LVEF improved with an average increase of 8%, and the post-procedural LVEF consisted of an rEF in 27 (16%), mrEF in 41 (24%), and pEF in 102 (60%) patients. During a median follow-up of 31 months, a total of 22 (13%) patients experienced the composite outcome, including 18 (11%) HFHs and 10 (6%) all-cause deaths (5 with cardiac issues, 2 any malignancies, and 3 other issues). In the Kaplan-Meier analysis using a Bonferroni correction, there was a significant difference in achieving the outcome between the rEF and mrEF, and rEF and pEF, but not between the mrEF and pEF groups (Figure). In a univariate analysis, the hazard ratio of the outcome was shown as follows: an age ≥ 65 years (hazard ratio, HR: 3.4 [95% confidence interval, CI: 1.4–8.5], p = 0.006), history of HFHs for AF (HR: 1.7 [95%CI: 0.7–4.0], p = 0.25), known underlying heart disease (HR: 1.9 [95%CI: 0.8–1.2], p = 0.13), pre-procedural LVEF < 40% (HR: 3.1 [95%CI: 1.3–7.5], p = 0.009), atrial tachyarrhythmia recurrence (HR: 3.0 [95%CI: 1.2–7.8], p = 0.01), and the post-procedural LVEF category (mrEF and rEF, compared with pEF) (HR: 2.0 [95%CI: 0.4–7.7], p = 0.34; and HR: 8.6 [95%CI: 2.7–37.5], p < 0.0001). Furthermore, in a multivariate analysis, patients with a rEF was the sole independent predictor of the composite outcome after adjusting for confounders including an age≥65 years and pre-procedural LVEF < 40% (HR: 12.0 [95%CI: 3.9–40.0], p < 0.0001), whereas those with a mrEF was not (HR: 1.8 [95%CI: 0.4–7.3], p = 0.42), as compared to those with a pEF. Conclusions Patients with a mrEF had a comparable prognosis to those with a pEF in a relatively long follow-up, while those with a rEF had the poorest outcome of the three categories, regardless of the pre-procedural LVEF severity. Abstract Figure. The difference in the rate of outcome