Objective To determine if fetal stem cells can enter the maternal circulation during pregnancy and repair the injuries of maternal heart. Methods C57 female mice at the age of 6-8 weeks were randomly assigned to three groups:sham control, surgery without pregnancy, and surgery with pregnancy (n=8,eath group). The control sham group was developed by opening and closing of the chest. The other two groups underwent heart surgery. The myocardial infarction (MI) model was induced by ligation of the left anterior descending coronary artery. Half of the surgical mice mated with e-GFP transgenic male mice, and another half group was not. Electrocardiogram (ECG) and echocardiographic images were recorded at pre-operation, post-operation and postpartum.The collected data were used to evaluate the heart function. The GFP expression was detected by immunohistochemistry and q-PCR.Results When compared with the sham group, both the ischemia surgery groups with and without pregnancy, the ECG ST segment was significantly increased. This measurement indicated that the myocardial ischemia surgery was successful, and no significant difference in the ST segments between two ischemia surgery groups was found. However, when ECG was measured in the surgical mice after postpartum, their myocardial ischemia was dramatically improved when compared with that of the ischemia surgery only mice. Echocardiographic images also indicated that both the surgery groups had myocardial ischemia, however, no significant difference was observed in the pregnant mice before and after postpartum. The order of the cardiac function indexes from high to low was the sham group, surgery with pregnancy group, and surgery with no pregnancy group; in particular, the cardiac function of pregnancy group was significantly enhanced compared with that of the surgery with no pregnancy group (P<0.05). More importantly, both immunofluorescence and q-PCR results showed that the embryonic stem cell translocation through circulation system with GFP expression in the heart of pregnancy group, while negative in other two groups. Conclusions Embryonic stem cells can be transferred into the maternal circulation of pregnant mice, and play a role in the repairing of their cardiac injuries.