The arterial bulb forms the trabecular portion of the right ventricle.

The junction between the ventricle and the arterial bulb will be called the primary intra-ventricular hole.

Initially the atrioventricular canal gives access to the primitive left ventricle, and is separated from arterial bulb by the edge of the ventricular bulb.

The tube is divided into cardiac regions along its craniocaudal axis: the primitive ventricle, called primitive left ventricle, and the trabecular proximal arterial bulb, called the primitive right ventricle.