This video explains the formation of all the parts of the interventricular septum in sufficient details with the mention of origin of each part and at the end discussing briefly about the ventricular septal defects. Timeline: 0:00 - Introduction 0:43 - Short overview of heart tube development 4:51 - Interventricular sulcus 6:04 - Formation of septum intermedium 7:00 - Formation of muscular part of interventricular septum 7:47 - Formation of membranous part of interventricular septum 9:03 - Filling of interventricular foramen 10:06 - Summary of parts of septum 11:06 - Atrioventricular septum 14:24 - Ventricular septal defects (VSDs)