Most commonly with tricuspid atresia the great vessels are normally related (TA with NRGV). This means that the pulmonary artery arises from the hypoplastic right ventricle and the aorta from the left ventricle. A ventricular septal defect (also referred to as a bulboventricular foramen) is required to ensure flow into the hypoplastic right ventricular chamber and subsequently to the lungs. Too large of a VSD may result in too much pulmonary blood flow (pulmonary overcirculation). A small restrictive VSD may result in too little pulmonary blood flow (cyanosis).