Background: Among all cardiovascular illnesses, myocardial infraction is regarded as one of the major causes of morbidity and death. Though, mortality rates have been reduced all over the past few years, there is still a relative risk for occurrence of the different major adverse cardiac events (MACEs). Objective: To evaluate the role of ratio of systolic blood pressure to left ventricular end-diastolic pressure at the time of primary percutaneous coronary intervention (PPCI) to predict MACEs both in-hospital and during 3-months follow up in patients with STEMI. Patients and Methods: This was a multicenter prospective study, conducted in Nasr City Health Insurance Hospital and Benha University Hospital in the period from March 2022 to March 2023. Included 100 patients who were presented by acute STEMI and managed by successful PPCI for a single vessel disease. Results: In our results, there was no statistically significant difference between the 2 groups as regarding demographic data and risk factors. Patients with MACEs had higher incidence of door to balloon time > 90 minutes, higher incidence of Killip class II and III, and of anterior STEMI in comparison with those without MACEs. Also, patients with MACEs had lower SBP and DBP, higher HR, lower LVEF, higher LVESV, higher incidence of DD grade II and lower both mean septal and lateral e' wave velocities, higher mean E wave velocity, both septal and lateral e/e' ratios. Patients with MACEs also had higher TIMI and GRACE RS, LVEDP, higher incidence of LAD as a culprit vessel. While, they had lower invasive SBP, DBP and SBP/LVEDP ratio. Regarding ROC curve analysis, SBP/LVEDP ratio cutoff value of ≤ 4.7 was shown to have the best diagnostic accuracy. TIMI risk score cut-off value > 3 was shown to have the second diagnostic accuracy in prediction of MACEs. AUC of SBP/LVEDP ratio was higher than that of TIMI RS, so SBP/LVEDP ratio was more accurate in predicting MACEs in STEMI patients who underwent primary PCI to a single vessel disease. Conclusion: SBP/LVEDP ratio is an easily rapidly determined ratio at the time of PPCI that can provide important prognostic