Objective To evaluate the effect of smooth muscle cell transplantation on myocardial interstitial reconstruction shortly after myocardial infarction. Methods A total of 48 female Wister rats were randomly divided into two groups with the random number table, the control group (n=24) and the smooth muscle cell transplantation group (n=24). The left coronary artery was ligated to set up the myocardial infarction animal model. An amount of 05 ml phosphate buffered saline(PBS) containing 1×106 smooth muscle cells or 0.5 ml PBS without cells was injected into the injured myocardium immediately. By immunoblot and reverse transcriptionolymerase china reaction (RT-PCR), we observed the amount of protein and mRNA of matrix metalloproteinase2(MMP-2), matrix metalloproteinase-9(MMP-9) and tissue inhibitor of metalloprotease-3 (TIMP-3) in the myocardium of the rats. Results The transplanted smooth muscle cells survived well. Compared with the control group, myocardial TIMP3 mRNA (1.06±0.22 vs. 0.81±0.19, t=－2.358, P=0.033) and protein content (3.33±0.53 vs. 1.63±0.47, t=－6.802, Plt;0.001) were significantly increased in the transplantation group. Myocardial MMP-2, MMP-9 mRNA (0.49±0.12 vs. 1.16±0.18, t=8.453, Plt;0.001; 0.45±0.12 vs. 0.80±0.11, t=5.884, Plt;0.001) and protein content (3.98±1.08 vs. 6.05±0.91, t=4.139, P=0.001; 0.39±0.14 vs. 0.57±0.17, t=2.409, P=0.031) [CM(1585mm]were significantly reduced in the transplantation group compared with the control group. Conclusion transplanted smooth muscle cells can survive well in the infarction myocardium and can increase the amount of myocardial TIMP-3 mRNA and protein content and reduce myocardial MMP-2, MMP-9 mRNA and protein content, which is an effective way to prevent harmful cardiac remodeling.