A case of conjoined thoracopagous twins with a shared atrial myocardium who were successfully surgically separated is described. Twin B had hypoplastic right heart syndrome and was dependent on Twin A for oxygenation of her blood. The twins were surgically separated by dilating Twin B's ductus arteriosus with an infusion of prostaglandin E1 and creating an aortopulmonary shunt to increase her pulmonary blood flow; both twins survived the operation. However, 1 week after surgery Twin B had hepatic and renal failure and died.