Background: Early improvement of perfusion after acute MI will improve left ventricle function and decrease the infarction area, thus decreasing mortality. Methodology:  52 patients presented with acute ST segment elevation MI Who underwent primary PCI within 24 hours of presentation. All patients were subjected to full history taking, physical examination, serial ECG, cardiac enzymes, calculation of relative importance index (RII)  by dividing culprit segment diameter by left anterior descending , circumflex and right coronary arteries at their proximal segments and myocardial perfusion  image to detect infarction size.            Results: There is significant correlation between RII and left ventricular dysfunction  (p: 0.028).  Significant correlation between RII and mortality are present. Conclusion: RII is significantly correlated with adverse clinical outcome in patients with acute STEMI.