Abstract Background the main therapeutic strategy for acute ST segment elevation myocardial infarction (STEMI) is the rapid restoration of epicardial blood flow in the infarcted related artery (IRA). Primary percutaneous coronary intervention (pPCI) is the most effective and recommended therapeutic intervention for the reperfusion strategy. Aim of the Work to investigate the incidence of QRS fragmentation among successfully revascularized inferior STEMI patients including single lead fragmentation (sl-fQRS) and classic QRS fragmentation (fQRS) and the prognostic importance of (sl-QRS) in patients with inferior STEMI who achieved TIMI 3 flow by primary PCI and its relation to results of angiography, poor prognosis prediction including in hospital mortality and Major Adverse Cardiac Events (MACE). Patients and Methods this prospective cohort study was carried out on 150 patients with successfully revascularized inferior STEMI patients by primary PCI, Patients were recruited postoperative from cardiology department, Ain Shams University Hospitals after undergoing Coronary Angiography for myocardial infarction which is the standard of care for such patients for follow-up during the study period (6 months). All patients were given informed consent. The study protocol was approved by the ethical committee, Faculty of Medicine, Ain Shams University. Results 150 patients with acute myocardial infarction, who were referred to the cardiology department for primary PCI, were eligible to participate in the study. Their mean age was 54.45 ± 11.11 years old. Most of them were males (78.7% of patients, 118 patients). 95 patients (63.3% of patients) had history of smoking wether current or ex-smokers. Nearly, one third of patients (34.7% of patients, 52 patients) were diabetic. Similarly, 34.7% of patients (52 patients) were dyslipidemic. 43.3% of patients (65 patients) were hypertensive. Their mean BMI was 26.69 ± 2.65 kg/m2. Most of patients (76.7% of patients, 115 patients) had positive family history. Conclusion The concept of at least two derivations is mentioned for the classical definition of fQRS, and only one lead with fQRS has not been accepted for the presence of fQRS. However, we showed that sl-fQRS is associated with MACE and higher risk. Therefore, instead of the concept of at least two derivations, the presence of fQRS in only one lead and/or ≥1 leads with fQRS may also be enough when describing the patients under high cardiac risk.