Abstract: The purpose of this research is to investigate the therapeutic effects of losartan potassium on 5/6 nephrectomy rats with chronic heart failure(CHF)and to explore the mechanism. 24 Rats were randomly divided into three groups namely sham group(Sham), pathology group(Nx)and losartan potassium group(Lst), respectively. CHF model in rats were induced by 5/6 nephrectomy. At the 7th week, rats of Lst group were given losartan potassium(50 mg/L)for consecutive 2 weeks. Then all rats were measured for hemodynamic parameters, cardiac index, creatinine, urea nitrogen in serum, and expressions of CD133, VEGFR2, Sox2, cleaved Caspase-3 and Bcl-2 in heart. Compared with Nx group, rats of Lst group improved cardiac and renal functions: decreased LVDP, LVEDP, cardiac index, creatinine, urea nitrogen and increased LVSP. Furthermore, losartan potassium up-regulated gene expression of CD133, VEGFR2, Sox2 and protein level of Bcl-2, and down-regulated cleaved Caspase-3 protein expression. Results suggest that losartan potassium can improve cardiac function of rats with CHF which may be correlated with mobilizing bone marrow stem cells, increasing endothelial progenitor cells(EPCs)level in heart, repairing endothelial function, and inhibiting myocardial apoptosis.