Type I: The defect is more proximal located between the origin of the main pulmonary artery and the ascending aorta immediately above the sinus of Valsalva (deficient septation of the aortopulmonary trunk). These defects tend to be large, round or oval shaped.
Type II: The defect is more distal, between the ascending aorta and the origin of the right pulmonary artery (abnormal migration of the 6th aortic arch). These defects are more rare and tend to be smaller in size.
Type III: A large defect combining the other two types