1. First, extensive investigations in patients with increased portal venous pressures, usually from cirrhosis, has shown that increased portal venous pressures lead to significant increases in the excretion of a wide variety of small peptide signaling molecules. Included in these molecules are VIP, 5-HT and Substance P.As patients with Fontan physiology always have increased portal and gut venous pressures as a direct consequence of their anatomic palliation, it stands to reason that they should likewise have increased GI production of these signaling peptides.