Background: In individuals with ST-segment elevation myocardial infarction, the most telling sign of arrhythmogenesis was a lengthening of the Tpeak-Tend (Tp-e) interval. Objective: To evaluate the Tpeak-Tend/ QT ratio in predicting malignant arrhythmias among cases who had myocardial infarction (elevated ST segment) and underwent primary percutaneous coronary intervention. Subjects and methods: In a prospective cohort study; we classified the selected cases into 2 groups: Group A: included 78 cases with complete-ST segment resolution (CSTR), which meant they got a successful complete reperfusion. Group B: included 42 patients with incomplete-STR (ISTR), meant they got an unsuccessful complete reperfusion. Results: Significant lower values of ST elevation, ventricular rate, and QT interval were found among CSTR group than ISTR group, significant lower corrected QT was found among CSTR group than ISTR group. Significant lower Tp-Tec, and Tp-e/QT ratio were found among CSTR group than ISTR group. AUC of ROC curve of Tp-e/QT and Tp-Tec were 0.746, 0.838. At cutoff ≥ 0.305 and ≥ 133.5, the sensitivity was 55.0% and 85.7% and specificity was 62.8% and 64.1% respectively. Conclusion: The electrophysiologic feature that represents transmural dispersion of cellular repolarization (TDR) in STEMI was similar in nature for both an elevated ST-segment and an elevated Tp-ec. Patients with STEMI after PPCI had an increased STR and Tp-e/QT ratio, both of which predicted arrhythmia and had predictive value for malignant arrhythmia.