Background : The transmural extent of acute Q-wave myocardial infarction(MI) remains uncertain. An application of new technique in cardiac magnetic resonance imaging(MRI) makes it possible to determine the transmural extent of MI. We evaluated the relation between cardiac MRI findings and electrocardiographic findings in acute myocardial infarction(AMI). Methods : Cine and contrast-enhanced cardiac MRI were performed within 3 days after admission in 34 AMI patients. The transmural extent and wall thickening were determined using a 32-segment model. We coined the myocardial necrosis score index(MNSI) that can be derived by dividing the sum of hyperenhancement score by the number of segment with abnormal wall motion and applied it to our study. In the same day of cardiac MRI examination, All electrocardiograms were acquired . The presence of Q wave was assessed by the criteria of Minnesota code. Infarct related artery was determined by coronary angiography in all patient. Results : Baseline characteristics were similar between Q-wave group(n=24) and non-Q-wave group(n=10). MNSI were significantly higher in Q-wave group than in non-Q-wave group (0.50짹0.22 vs. 0.28짹0.28, p<0.05). MNSI of ST elevation group is significantly higher than of non-ST elevation group(0.54짹0.19 vs. 0.26짹0.26, p<0.01). Conclusion : The transmural extent of acute Q-wave MI is higher than that of non-Q-wave MI. MNSI of acute Q-wave MI represents approximately 50% of transmural extent, that is actually non-transmural. Transmural extent of ST elevation AMI is approximately 54%