Background The requisite techniques for safe fetal cardiac arrest during cardiac interventions need to be further developed. Furthermore, little is known about the pathophysiologic effect of cardiopulmonary bypass(CPB)at different levels of temperature with cardioplegic arrest on the developing fetus. Methods Twelve pregnant goats were randomly divided into hypothermic CPB group(H group): cardiopulmonary bypass with perfusion at 30-32℃(n=6) and normothermic CPB group(N group): cardiopulmonary bypass with perfusion at 36℃-38℃(n=6). Fetal cardiopulmonary bypass was maintained including 30 minutes of cardiac arrest. Fetal mean arterial blood pressure(MAP) and heart rate(HR) were monitored. Fetal arterial blood samples were analyzed. The pulse index(PI) and resistance index(RI) of the fetal umbilical artery were recorded. Results The maternal weight,fetal weight and pump flow had no significant difference between the 2 groups. After clamp removal, two fetal hearts did not auto-beat in H group. The fetal HR and MAP b were significantly different(P<0.05) etween the 2 groups. There was remarkable decreasing in post-CPB fetal HR and MAP in H group. A stable decrease in partial pressure of oxygen with a concomitant stable increase of carbon dioxide partial pressure in H group was noted.The lactic acid in H group was significantly higher than that in the N group(P<0.05). The PI and RI in H group were significantly elevated 1 hour after off CPB and further markedly increased 2 hours after off bypass. Conclusions Fetal CPB could be performed under both hypothermic and normothermic conditions. However, normothermic bypass may provide better delivery of oxygen to fetal tissue. Background The requisite techniques for safe fetal cardiac arrest during cardiac interventions need to be further developed. Furthermore, little is known about the pathophysiologic effect of cardiopulmonary bypass (CPB) at different levels of temperature with cardioplegic arrest on the developing fetus. Methods Twelve pregnant goats were randomly divided into hypothermic CPB group (H group): cardiopulmonary bypass with perfusion at 30-32 ° C. (n = 6) and normothermic CPB group (N group): cardiopulmonary bypass with perfusion at 36 ° C.-38 ° C. (n = 6) Fetal cardiopulmonary bypass was maintained for 30 minutes of cardiac arrest. Fetal mean arterial blood pressure (MAP) and heart rate (HR) were monitored. The pulse index (PI) and resistance index (RI) of Results The maternal weight, fetal weight and pump flow had no significant difference between the 2 groups. After clamp removal, two fetal hearts did not auto-beat i nH group. The fetal HR and MAP b were significantly different (P <0.05) etween the 2 groups. There was remarkable decrease in post-CPB fetal HR and MAP in H group. A stable decrease in partial pressure of oxygen with a concomitant stable increase of carbon dioxide partial pressure in H group was noted. The lactic acid in H group was significantly higher than that in the N group (P <0.05). The PI and RI in H group were elevated elevated 1 hour after off CPB and Further markedly increased 2 hours after off bypass. However, normothermic bypass may provide a better delivery of oxygen to fetal tissue.