Post-operative arrhythmias are most often transient and medically treated, but some patients may require electrophysiology study (EPS) and ablation. To describe the efficacy and safety of early post-operative ablation. Retrospective series of patients who underwent EPS within 12 months of surgery for congenital heart disease (CHD) between 2000-2021. Procedural outcome included complete or partial success, failure or empirical ablation and complications. Long-term outcome included arrhythmia recurrence and burden according to a 12-point clinical arrhythmia severity score (documented arrhythmia, arrhythmia severity, cardioversion, antiarrhythmic medication). From 28,902 surgeries during the study period, 24 (0.1%) patients 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%) CHD complexity. Mechanisms of arrhythmias included intraatrial 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%). Procedure was acutely successful in 41 (82%) patients, empiric in 5 (10%) and unsuccessful in 4 (8%). Complications occurred in 4 patients (major in 1, moderate in 1, minor in 2). Recurrence of arrhythmia was documented in 27 (54%) patients, although the burden of arrhythmia was significantly reduced. A minority of patient require early post-operative 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.