Abstract: To study the effects of hypothermia on the fetal lamb during tetal cardiopul-monary bypass. 12 pregnant goats （120-140 days gestation） were divided into two groups：one group for fetal normothermic bypass （37℃，n= 6），the other group for fetal hypothermic bypass （28℃，n= 6）. The circuit consisted of roller pump and artificial oxygenator. Fetal bypass lasted one hour. The blood gas, heart rate and blood pressure were monitored for the goats and fetal lamb. During hypothermic bypass, heart rate of fetus slow down,the pH of blood were decreased gradually following bypass. After fetal lamb wean off bypass, degrees of hypoxia, hypercarbia, acidosis in the hypothermic group were much stronger than that of normothermic group. Heart rate and blood pressure reduced seriously in hypothermic group after bypass. In conclusion，hypothermia is detrimental to the fetal-placental unit during fetal cardiopulmonary bypass.

Key words: Fetal lamb, Hypothermia, Cardiopulmonary bypass