This defect consists of a complete obstruction of the right ventricle outflow tract due to a hypoplastic (narrowed) pulmonary artery. When the ventricular septum is intact the PDA and / or bronchial collateral arteries provide the only source of pulmonary blood flow. There are two types of this defect: A small right ventricle with a thick wall and a small but working tricuspid valve. This is the most common. The other type is to have a normal right ventricle with a complete but malfunctioning tricuspid valve.