Ventricular septation begins at 4th week and is completed by the end of 7th week.
Upper membranous part of septum arises from the endocardial cushion, conotruncal ridge and grows downward. Lower muscular part of septum appears from the floor of ventricles and grows upward.
The majority of the septum is made up of the muscular part. Failure in the fusion of upper and lower septum will lead to ventricular septal defect.
The endocardial cushion also contributes to the development of all valves and play a significant role for intra-heart partitions. Various neural crest cell abnormalities will affect cardiac septal development.
Adapted from: Fundamentals of Cardiology: Concise Review for USMLE and General Medical Boards Image source: www.keyword-suggestions.com