Background and objectives : An early invasive strategy with coronary revascularization is currently the recommended treatment for patients at high risk with acute non-ST-segment elevation myocardial infarction (NSTEMI). We estimated myocardial injury by cardiac magnetic resonance(CMR) according to the timing of percutaneous coronary intervention(PCI) in intermediate and high risk NSTEMI. Subjects and Methods : This study enrolled 39 patients who had intermediate and high risk NSTEMI and had peak CK-MB above 50ug/L. Patients were stratified by the time interval from chest pain onset to PCI. (Group I: <24hr, n=10; Group II: 24-48h, n=12; Group III: >48h n=17). All patients also underwent 1.5T (Avanto, Siemens) CMR 15 minutes after the injection of gadopentetate dimeglumine (Magnevist, Bayer) using phase sensitive inversion recovery sequences. The percentage of infarct area to the total area of myocardium was calculated. Results : Baseline characteristics were not different statistically among three groups. TIMI risk scores were not difference among three groups(Group I: 3.6; Group II: 2.8; Group III: 3.4). Mean Peak CK-MB, Peak troponin-I were 118.1 ug/L, 30 ng/ml. The percentage of infarct area to the total area of myocardium by CMR was no difference among three group(Group I: 17.4짹14.6% ; Group II: 11.3짹9.5%; Group III: 21.0짹 10.5%, p=0.278). Conclusion : In high and intermediate risk acute NSTEMI, degrees of myocardial injury by CMR according to the timing of PCI were similar.