Abstract: Objective To observe the expression of S100A4 and to study the effect of S100A4 on cardiac muscle injury induced by exhaustion exercise.Methods Twelve male Wistar rats were divided into two groups:control group (CN)and exhaustion exercise group(EI).After 10 days of exhaustion exercise,the rats in both CN and EI were immediately decapitated and their blood and cardiac muscle samples were collected.The histology of cardiac muscle were detected with lightmic roscope and transmission electron microscope.The expressions of S100A4 prote in were detected with western blot and mimunoh istochem istry.Results The observation of light micro scope showed that there were vacuolar degeneration or interstitial edema in myocardium and endothelial cells of EI group.The transm ission electron micro scope observation revealedendo the lial cells apoptosis after exhaustion exercise.Western blot results proved that the expression of S100A4 in CN group was low and the expression of S100A4 of EI group increased.Immunoh isto chemistry results showed that the expression of S100A4 incresed by 1.68 folds and was distr ibuted in both myocardial cells and endo the lial cells afte rexhaustion exercise.Conclusion Exhaustion exercise could induce cardiac muscle injury and increase the expression of S100A4 in cardiac muscle in rat.