BACKGROUNDIschemic heart disease (IHD) has been linked to an increased risk of atrial fibrillation (AF). However, data are sparse regarding the role of IHD in AF recurrence after catheter ablation.OBJECTIVEWe sought to investigate whether preexisting or new-onset IHD is associated with a greater risk of AF recurrence after ablation.METHODSWith use of Danish nationwide registries, all patients undergoing first-time AF ablation in Denmark from 2010 to 2020 were identified. The primary outcome was AF recurrence defined by AF-related hospital admission or antiarrhythmic drug use within 1 year after ablation excluding a 3-month blanking period. IHD was defined as an International Classification of Diseases, Tenth Revision diagnosis of IHD or prior coronary revascularization.RESULTSOf 12,162 patients undergoing first-time ablation for AF (mean age, 62 years; 30% female), 20% had preexisting IHD. Preexisting IHD was associated with an increased risk of AF recurrence in univariable log-binomial logistic regression (relative risk, 1.09; 95% CI, 1.04-1.14; P < .001). However, after multivariable adjustment including procedural year, preexisting IHD was no longer associated with an increased risk of AF recurrence (relative risk, 1.02; 95% CI, 0.97-1.06; P = .42). In a nested case-control study of those without preexisting IHD before ablation (n = 9778), newly diagnosed IHD after ablation was associated with an increased risk of AF recurrence in multivariable analysis (hazard ratio, 3.03; 95% CI, 1.84-4.99; P < .001).CONCLUSIONThe presence of IHD does not appear to reduce the effectiveness of AF ablation procedures. However, the emergence of IHD after AF ablation may serve as a trigger for AF that is insufficiently suppressed by prior ablation.