Background: Mitral regurgitation(MR) after myocardial infarction(MI) is closely related with an adverse prognosis and increase mortality even when mild. In recent studies. Mild to moderate MR after AMI diagnosed by echocardiography were independently associated with increased 1-year mortality. The aim of this study is to evaluate the effect of MR after AMI to the LV, LA dimension, and LV diastolic function. Method: 1,100 patients were enrolled in this registry, Among them 425 patients who performed follow up echocardiography were enrolled in this study. After primary PCI or thrombolytic therapy, 1st echocardiogrphic exam was performed and 6 months later 2nd echocardiography was done. In follow-up Echocardiography, patients with no MR or trivial MR were grouped as Group 1 and more than mild MR were grouped as a group 2. We compared the LVESD, LVEDD, LAD, mitral E/A ratio, E/E, changes of MR degree of 1st and 2nd Echo findings and clinical data, Result: 1) Male were 323(76%), Mean age was higher in group 2(60.1짹11.9 group 1, 63.9짹12.2 group 2). 2) In clinical findings, Group 2 showed higher creatinine kinase level(988짹1537, 1526짹2106, respectively, p<0.05), however, blood pressure, heart rate, post-TIMI score, location of IRA, Killip classification were not different in both groups. 3) Aggravation of MR was more frequent in group 2 (50%, Gr2 vs 7%, Gr1, p<0.0001). Other Echo paramenter were as follows 4) MACE(death, MI, CHF) was higher in group 2 (5.3%) than group 1(2.2%) Conclusion: MR after myocardial infarction might influence LV function and remodeling.