Contraindications
After Fontan, blood must flow through the lungs without being pumped by the heart. Therefore children with high pulmonary vascular resistance may not tolerate a Fontan procedure. Often cardiac catheterization is performed to check the resistance before proceeding with the surgery. (This is also the reason a Fontan procedure cannot be done immediately after birth; the pulmonary vascular resistance is high in utero and takes months to drop.)
Read more about this topic: Fontan Procedure