The Norwood procedure is the first surgery of three staged heart surgeries to create a new functional systemic circuit in patients with hypoplastic left heart syndrome or other complex heart defects with single ventricle physiology. The Norwood procedure (stage 1) involves atrial septectomy and transection and ligation of the distal main pulmonary artery. The proximal pulmonary artery is then connected to the hypoplastic aortic arch, while the coarcted segment of the aorta is repaired. An aortopulmonary shunt is created to connect the aorta to the main pulmonary artery to provide pulmonary blood flow. The second surgery (Stage 2) is the separation of the systemic and pulmonary circulation once pulmonary vascular resistance has fallen, by removing the aortopulmonary shunt followed by the creation of a bidirectional SVC-pulmonary shunt, also known as a modified Glenn procedure or Hemi-Fontan. The third surgery (Stage 3) is the Fontan procedure, in which the inferior vena cava (IVC, the large vein carrying blood back to the heart from the lower part of the body) is connected to the branch pulmonary arteries. After this surgery is completed, all the venous blood returning from the body flows directly to the lungs.