Stage II of the Norwood procedure, also known as the hemi-Fontan or bidirectional Glenn procedure, is typically performed when the infant is between three and nine months of age. It connects the superior vena cava (the large vein that collects oxygen-poor blood from the upper part of the body) directly to the pulmonary artery. This new pathway allows oxygen-poor blood from the head and upper body to flow directly to the lungs, bypassing the heart and defective ventricle. Once the blood receives fresh oxygen in the lungs, it goes back to the heart and is pumped out to the body.

At this stage, the Blalock-Taussig shunt or Sanno procedure is removed because oxygen-rich blood can now circulate throughout the body. This is a crucial step in avoiding the mixing of red (oxygen-rich) and blue (oxygen-poor) blood. However, the complete operation is only half-finished because the oxygen-poor blood returning from the lower part of the body has not yet been re-routed. After this stage, the baby will still have a bluish tinge, but will be better able to handle infection and other problems.