Abstract Background: Terminal QRS complex distortion on admission electrocardiography (ECG) has been used to estimate the final infarct size and the prognosis after acute coronary syndrome (ACS); however, it is not sure whether the QRS distortion is more reliable for predicting the severity of coronary artery lesions or not. The Aim of the Work: The aim is to analyze the admission ECG in ACS based on abnormality observed in the terminal QRS complex distortion and ST-segment and its relation to coronary artery lesion severity. Patients and Methods: We included 150 patients presented with ACS. Patients were divided according to the presenting ECG in two major groups, 120 patients presented with ST-segment elevation myocardial infarction (STEMI) who were classified into two groups according the presence or absence of the QRS distortion: 42 patients with +ve QRS distortion (Group I) and 78 patients with −ve QRS distortion (Group II), and 30 patients presented with non-ST-segment elevation (NSTE)-ACS who were also further classified according the magnitude of ST shift by millimeter into three groups. All patients underwent primary percutaneous coronary intervention, and Gensini score defined the severity of coronary artery lesions. Results: In this study, in STEMI patients groups, we observed that QRS distortion on admission, ECG has a significant relationship with high Gensini score values, whereas in NSTE-ACS patients, we demonstrated no significant difference between the extents of ST-segment shift and Gensini score values. Conclusion: QRS distortion has a significant value in predicting severe coronary artery lesions in STEMI patients while the extent of ST-segment shift has no benefits in predicting the severity of coronary artery lesion in NSTE-ACS patients.