The relationship between pre-ablation left ventricular diastolic dysfunction (LVDD) and prognosis in patients with left ventricular systolic dysfunction (LVSD) undergoing atrial fibrillation (AF) ablation remains unclear. The prognosis of 173 patients with impaired left ventricular ejection fraction (<50%) who underwent AF ablation was examined. The primary outcome was a composite of all-cause mortality, heart failure (HF) hospitalization, and worsening HF symptoms requiring unplanned outpatient intensification of decongestive therapy. During the follow-up period (median, 3.5years), the primary outcome after AF ablation occurred in 28 patients (16%). The receiver operating characteristic curve analysis showed that early septal diastolic mitral annular velocity (e') had a larger area under the curve (0.70) than other LVDD parameters, and optimal cut-off values of LVDD, represented by e', septal E (early diastolic left ventricular filling velocity)/e', and peak tricuspid valve regurgitation velocity (TRV), were 5.0cm/s, 13.2, and 2.5m/s, respectively. Multivariate analysis revealed that e' ≤5.0cm/s (standard hazard ratio [HR], 3.87; 95% confidence interval [CI], 1.73-8.69; p=0.001), septal E/e' ≥13.2 (HR, 3.62; 95% CI, 1.60-8.21; p=0.002), and peak TRV≥2.5m/s (HR, 2.42; 95% CI, 1.13-5.16; p=0.02) independently predicted the outcome. Patients with New York Heart Association functional status≥III had a 3.3-4.5-fold higher risk of the outcome. LVDD or severe HF symptoms predict poor outcomes in patients with LVSD undergoing AF ablation. Therefore, patients with LVDD or severe HF symptoms should receive more intensive treatment even after AF ablation.