BACKGROUND : The prevalence of atrial fibrillation (AF) is on the rise in the aging population with congenital heart disease (CHD). A few case series have described the feasibility and early outcomes associated with radiofrequency catheter ablation of AF centered on electrically isolating pulmonary veins (PV) in patients with CHD. In contrast, cryoballoon ablation has not previously been studied in this patient population despite its theoretical advantages, which include a favorable safety profile and shorter procedural time. OBJECTIVE : To assess the safety and feasibility of cryoballoon ablation for AF in an initial cohort of patients with CHD. METHODS : The study population consisted of consecutive patients with CHD and cryoballoon ablation for AF at the Montreal Heart Institute between December 2012 and June 2017. Procedural complications, acute success, and 1-year freedom from recurrent AF after a single procedure with or without antiarrhythmic drugs were assessed. Procedures were performed under conscious sedation. Left atrial access was obtained via a single transseptal puncture or through an existing atrial septal defect (ASD). Cryoballoon occlusion was assessed by distal injection of 50% diluted contrast into the pulmonary vein. At least one 240-second cryothermal application was performed upon obtaining complete pulmonary vein occlusion. Following ablation, patients were routinely followed at outpatient visits at 1, 3, 6, and 12 mo, and then annually. RESULTS : Ten patients, median age 57.9 (interquartile range 48.2-61.7) years, 60% female, met inclusion criteria and were followed for 2.8 (interquartile range 1.4-4.5) years. Two had moderately complex CHD (sinus venosus ASD with partial anomalous pulmonary venous return; aortic coarctation with a persistent left superior vena cava), with the remainder having simple defects. AF was paroxysmal in 8 (80.0%) and persistent in 2 (20.0%) patients. The pulmonary vein anatomy was normal in 6 (60.0%) patients. Four had left common PV (n = 3) and/or 3 right PV (n = 2). Electrical pulmonary vein isolation (PVI) was acutely successful in all. One patient had transient phrenic nerve palsy that recovered during the intervention. No major complication occurred. One year after a single ablation procedure, 6 (60%) patients remained free from AF. One patient with recurrent AF had recovered pulmonary vein conduction and underwent a second PVI procedure. A second patient had ablation of an extra-pulmonary vein trigger for AF. CONCLUSIONS : Cryoballoon ablation for AF is feasible and safe in patients with simple and moderate forms of CHD, with an excellent acute success rate and modest 1-year freedom from recurrent AF.