Fig. 1
From: CT imaging features of atrioventricular shunts: what the radiologist must know
Primitive atrium and ventricle before the age of 30 days in a frontal view (a) and lateral view (b) and around 30 days in a frontal view (c) and lateral view (d). Before the age of 30 days, the embryonic heart is composed of a primitive atrium (A) and ventricle (V) without a dividing septum. Around 30 days of gestation the primary atrial septum or septum primum (SP, drawn in red), begins to grow as a crescent-shaped structure downwards from the roof of the primitive atrium toward the atrioventricular (AV) canal