Fig. 6
From: CT imaging features of atrioventricular shunts: what the radiologist must know
In the fifth embryological week, two ridges (drawn in orange and in green) develop in the wall of bulbus cordis. These ridges will converge in the midline and grow and extend toward the muscular interventricular septum (IVS), in a helical way. This leads to the formation of the aortopulmonary septum, which divides the bulbus cordis into two arterial channels, the aorta and the truncus pulmonalis, the former continuous with the left ventricle and the latter with the right ventricle. At the end of the seventh week, the ridges fuse with the atrioventricular (AV) endocardial cushions and with the muscular septum, forming the membranous septum and closing the interventricular foramen