Septation of truncus arteriosus will give rise to pulmonary artery and aorta.
Two processes take place in this septation:
Formation of the aortic-pulmonary septum: the septum will divide truncus arteriosus into two tubes. One tube will form pulmonary artery, and another tube will form aorta.
Spiral rotation: during the process of septation, initially pulmonary artery is on the left side and aorta is on the right side. Spiral rotation is necessary so that aorta ends up on the left side (to left ventricle) and pulmonary artery ends up on the right side (to the right ventricle).
Failure of aorticopulmonary septum development will result in truncus arteriosus while the failure of spiralization will result in transposition of great vessels.
If aorticopulmonary septum fails to align correctly and shifts anteriorly to right, it will result in tetralogy of Fallot.