Studies of blood gas and lung histopathology were done in 10 dogs after intrapericardlal aorto-right pulmonary arterial anastomosis with proximal ligation of the right pulmonary antery. Among the 5 expired during or after operation, in 3 cases, the causes of the death were due to surgical bleeding and, in 2 cases, acute cardiopulmonary insufficiency because of large anastomosis stoma measured respectively 7mm and 10mm. In the 5 of survivals, one was sacrificed because of empyema at postoperative 7 days and 2 were at postoperative one month and remained 2 at postoperative 3 month respectively. The following observations were made.