(A) Diagram showing the septal aspect of the right atrium and ventricle. The types of VSD (yellow shapes) are shown in relation to the course of the AV conduction tissues. The fibrous tissue (green) at the postero-inferior margin of the perimebranous VSD abuts the AV conduction bundle. (B) This diagram shows usual atrial arrangement with discordant AV connections with the morphologically LV opened. The AV conduction bundle passes antero-superior to the LV outlet and descends along the anterior margin of VSD. (C) The AV node is abnormally located. (D) The AV node is located in the muscular floor of the right atrium in hearts with ‘tricuspid atresia’ where there is absence of the right AV connection. (E) When viewed from the aspect of the rudimentary RV, the AV conduction bundle passes along the margin of the ventricular septal defect (VSD) that is nearest to the acute cardiac margin. AV, atrioventricular; VSD, ventricular septal defect; RV, right ventricle; LV, left ventricle; SCV, superior caval vein; ICV, inferior caval vein; MV, mitral valve.