Background: Treatment delay is considered to be one of the important predictors of survival in ST-elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PCI). We investigated the impact of early successful PPCI for STEMI patients on left ventricular ejection fraction. Methodology: This prospective study was carried out on 50 patients having STEMI undergoing PPCI in NICVD Karachi. Patients were divided into two groups, Group A, early presenter, patients received treatment with PPCI within six hours of the onset of symptoms, and group B, late presenter, patients received treatment after six hours up to twenty-four hours of the onset of symptoms. Results: Group A patients showed promising results, having achieved TIMI grade III flow in 100%, whereas 85% of patients achieved TIMI grade III flow in group B (P = 0.02). There was a statistical difference between the two groups. Using Independent sample T-Test Group A patients showed improved LVEF as compared to Group B (at presentation 45.49±3.99% vs. 35.25±3.85%; P = 0.001 and at 3 months follow up 55.66±0.92% vs. 45.75±1.44%; P = 0.001). Conclusion: Early PPCI treatment of STEMI patients can lead to improved TIMI grade flow and LVEF. Efforts must be made to shorten the delay in reperfusion therapy.