OBJECTIVES: We aimed to determine the incidence of postoperative complete atrioventricular block, the time to recovery or permanent pacemaker implantation, and the predictors for postoperative atrioventricular block after congenital heart surgery. METHODS: Patients who underwent open heart surgery from January 2001 to January 2024 were analyzed and predictors of atrioventricular block were identified using a logistic regression model. RESULTS: Among 9765 congenital heart surgeries, 333 (3.4%) were complicated by atrioventricular block, and 193 patients (1.9%) underwent permanent pacemaker implantation. The highest rates of atrioventricular block were found in patients who underwent repair of congenitally corrected transposition of the great arteries (27.3%), followed by Konno procedure (20.0%), and mitral valve replacement (16.0%), and arterial switch with closure of ventricular septal defect and arch repair (15.0%). In 134 (1.4%) patients with transient atrioventricular block, the median time to resolution was 4 days (interquartile ranges: 2-8 days). After 7 postoperative days, 75% had resolved, and after 12 postoperative days, 90% had resolved. Risk factors for the development of atrioventricular block were older age at operation (odds ratio: 1.012, p = 0.001), preoperative endocarditis (2.422, p <
0.001), longer aortic cross-clamp time (1.018, p <
0.001), and high-risk procedures (1.397, p = 0.012). CONCLUSIONS: Postoperative atrioventricular block is not rare after congenital heart surgery, with more than half of them needing permanent pacemaker implantation. Older age at operation, preoperative endocarditis, longer aortic cross-clamp time, and high-risk procedures were risks for the development of atrioventricular block. Pacemaker implantation should be delayed to the 12th postoperative day, when 90% of transient blocks have resolved.