Control group subjects (Group IV) will have normal hepatic-pulmonary blood flow and normal portal venous pressures. An atrial septal defect allows for left to right shunting of blood thru the heart but does not typically result in elevated pulmonary artery or right ventricular pressures. These subjects will have normal flow of hepatic venous blood into the pulmonary capillary bed. Therefore they should have normal hepatic production and pulmonary clearance of substance P and VIP.