Methods Six ewes underwent laparotomy. The fetal lambs were exposed by uterotomy and underwent median sternotomy. A 10 F arterial perfusion cannula was inserted into pulmonary artery and a 12~ 14 F venous cannula was put into right atrium. 方法选用6头怀孕山羊,切开子宫,暴露胎羊,正中开胸,经肺总动脉插10F动脉管,右心房插12~14F静脉管。