Background: The QT dispersion (QTd) can be used as effective reperfusion marker among cases who undergo primary Percutaneous Coronary Intervention (PCI) after having acute myocardial infarction. Objective: Study of the correlation between myocardial perfusion and QT dispersion on 12 lead surface ECG among patients who had acute ST-elevation myocardial infarction (STEMI) managed by primary PCI. Patients and methods: In a prospective cohort study, 100 cases admitted to the Cardiology Departments of Zagazig University Hospital and El-Zaitoun Specialized Hospital within 12 hours of symptom onset were recruited. This study included all patients who fulfilled the criteria for acute STEMI and were candidates for primary PCI. All cases underwent electrocardiogram (ECG), echocardiogram (ECHO), and coronary angiogram. Results: Myocardial electrical heterogeneity was rapidly restored to normal after effective reperfusion, whereas insufficient tissue reperfusion (Myocardial blush grade (MBG) lower or equal to 2) even with Thrombolysis in Myocardial Infarction (TIMI) III flow, was not related to the resolution of the increased QTd. QTd and corrected QTD (QTcd) were significantly shortened following recanalization of the infarct-related artery among cases with successful tissue-level myocardial reperfusion (MBG3). The pre-procedural QTd is a significant predictor of the patients' MBG (i.e., The MBG improves with lower pre-procedural QTd values and worsens with higher QTd values.) Conclusion: Effective revascularization of myocardial tissue was determined by MBG related to normal electrical heterogeneity restoration with reduction of QTd in the jeopardized myocardium. The pre-procedural QTd is a significant predictor of the patients' MBG. © 2022, Ain Shams University Faculty of Medicine. All rights reserved.