The study was to investigate the changes in matrix metalloproteinase-9 (MMP-9) and tissue inhibitors of metalloproteinase-1 (TIMP-1) in acute myocardial infarction (AMI) patients after percutaneous coronary intervention (PCI) and to explore their correlation to recent left ventricular remodeling (LVRM) and cardiac function. A total of 98 AMI patients were recruited of whom 51were admitted within 12 h and treated with PCI immediately (Group A), 22 were admitted at 12 h after AMI and treated with delayed PCI when the disease condition was stable(Group B), and the remaining 25 received conservative therapy(Group C). In Group D, 20 healthy subjects were enrolled. Two-dimensional echocardiography was performed to detect the end diastolic volume (EDV), end systolic volume (ESV), left ventricular ejection fraction (LVEF), left ventricular end diastolic diameter (LVDd) and ventricular aneurysm. In Group A, MMP-9 significantly increased after PCI, but returned to nearly normal level at 7 days after AMI. The MMP-9 level in Group A was markedly different from that in Groups B and C (P<0.05). At 90 days after AMI, examination revealed the EDV, ESV, LVDd and LVEF in Groups A and B were superior to those in Group C (P<0.05). The MMP-9 on day 7 was positively related to the EDV (r=0.261, P<0.05) and ESV(r=0.340, P<0.05) but negatively to LVEF (r=-0.218, P<0.05) on day 90. So we concluded that expression increases at early stage of AMI. During the LVRM, MMP-9 is positively associated with EDV and ESV but negatively with LVEF.