Aim To study whether erythropoietin(EPO)has effect on bone marrow KDR+ stem cells and the possible mechanism in mice with acute myocardial infarction(AMI).Methods Acute myocardial infarction mice were established by cryoinjury.Sixty male mice were randomly divided into four groups after cryoinjury:EPO group,AMD3100 inhibition group,control group,sham surgery group.The changes of KDR positive cells in peripheral blood were determined by flowcytometry.Immunohistochemisty was used to detect capillary density of peri-infarct area in 2 and 4 weeks after surgery.Results Compared with EPO group,the number of KDR positive cells in peripheral blood decreased in AMD3100 inhibition group(2.88%±0.67% vs 0.28%±0.13%,P><0.05).Two and four weeks after acute myocardial infarction modeling,the capillary density in EPO group was significantly higher than that in AMD3100 inhibition group and control group(P><0.05).But only 2 weeks after surgery,the capillary density in AMD3100 inhibition group was higher than that in control group(P><0.05).Conclusion EPO can effectively mobilize KDR+ stem cells from bone marrow to peripheral blood,which increased capillary density in peri-infarct area in mice with acute myocardial infarction.The effect can be completely restrained by AMD3100,which suggested that EPO may mobilize KDR+ cells in bone marrow to peripheral blood by SDF-1α/CXCR4 axis.