BACKGROUND A serious complication after surgical closure of ventricular septal defect (VSD) is complete heart block. In this retrospective study, we reviewed the incidence of complete heart block after surgical closure of a VSD at Great Ormond Street Hospital from 1976 to 2001 to identify any particular anatomic features that still predisposed patients to surgically-induced complete heart block and to provide anatomic guidelines to avoid this in future. METHODS Data were extracted from our local database for patients having (1) isolated VSD or VSD in the setting of (2) tetralogy of Fallot with pulmonary stenosis or (3) tetralogy of Fallot with pulmonary atresia; (4) absent pulmonary valve syndrome; (5 and 6) coarctation or interruption of the aortic arch; and (7) subaortic fibrous shelf. We carefully reviewed the operative notes from all patients with postoperative complete heart block to discover any predisposing anatomical reasons to explain the complication. RESULTS Two thousand seventy-nine patients had a VSD closure. Permanent complete heart block developed in 7 of 996 patients (0.7%) with an isolated defect and in 1 of 847 patients (0.1%) with tetralogy of Fallot. Four more patients had postoperative complete heart block. CONCLUSIONS Instances of iatrogenic complete heart block continue to occur after surgical VSD closure, either because of unexpected biological variations or because of unawareness of the disposition of the atrioventricular conduction axis in particular circumstances. This report emphasizes the latter aspect in details and suggests a risk of iatrogenic complete heart block of less than 1%.