BACKGROUNDPostoperative arrhythmias are most often transient and medically treated, but some patients may require electrophysiology study (EPS) and ablation.OBJECTIVEThe purpose of this study was to describe the efficacy and safety of early postoperative ablation.METHODSThis study presents a retrospective series of patients who underwent EPS within 12 months of surgery for congenital heart disease between 2000 and 2021. The procedural outcome included complete or partial success, empirical ablation or failure, and complications. The long-term outcome included arrhythmia recurrence and burden according to a 12-point clinical arrhythmia severity score (documented arrhythmia, arrhythmia severity, cardioversion, and antiarrhythmic medication).RESULTSAmong 28,902 operations during the study period, 24 patients (0.1%) underwent EPS within 3 months of surgery and 26 (0.1%) 3-12 months after surgery. Most patients had great (n = 27 [50%]) or moderate (n = 21 [42%]) congenital heart disease complexity. Mechanisms of arrhythmias included intra-atrial reentrant tachycardia (n = 23 [46%]), ectopic atrial tachycardia (n = 13 [26%]), accessory pathway (n = 6 [12%]), atrioventricular nodal reentrant tachycardia (n = 7 [14%]), twin atrioventricular node (n = 1 [2%]), atrial fibrillation (n = 1 [2%]), junctional ectopic tachycardia (n = 1 [2%]), and ventricular tachycardia (n = 2 [4%]). The procedure was acutely successful in 41 patients (82%), empirical in 5 (10%), and unsuccessful in 4 (8%). Complications occurred in 4 (8%) patients (major in 1, moderate in 1, and minor in 2). The recurrence of arrhythmia was documented in 27 patients (54%), although the burden of arrhythmia was significantly reduced.CONCLUSIONA minority of patients require early postoperative EPS and ablation. For those, the procedure can be performed with reasonable acute success and manageable morbidity even in critically ill patients with complex surgical anatomy.