Background: Pre-infarction angina (PIA) has not been thoroughly investigated in cases of primary percutaneous coronary intervention (PCI). The aim of this study was to clarify the impact of PIA on short term outcomes after ST elevation myocardial infarction (STEMI) treated by primary PCI. Methods: From Jan 2014 to June 2015, a total of 292 patients were recruited from the coronary care unit (CCU) of National Heart Institute (NHI) and prospectively evaluated for the study endpoints. These patients were divided into two groups: A: comprising 146 patients with PIA; and B: comprising 146 patients without PIA. On hospital admission, all patients gave a thorough history including the timing of their most recent anginal pains. All patients with an acute MI < 12 h in duration and who had been treated with primary PCI were included in this study. Transient typically ischemic chest pain that lasted less than 30 minutes in the last 24 hours before the onset of STEMI was considered PIA. All patients had a transthoracic 2D echocardiography studies during the index STEMI hospitalization and after discharge (1 month post STEMI) Results: Post discharge echocardiography study showed that patients with history of PIA had more significant improvement in wall motion score index (WMSI) compared to patients without history of PIA with significant p-value of 0.01. Comparing the change in pre and post PCI echocardiography study in both study groups, patients with history of PIA had significant improvement in left ventricular ejection fraction (LVEF) compared to patients without history of PIA with significant p-value of 0.001. Patients with PIA had lower maximum CKMB values compared to those without PIA. PIA patients had significantly less heart failure and ventricular tachycardia/ ventricular fibrillation events (VT/VF), p value of 0.03 and 0.04 respectively. Conclusion: This study provides further evidence of the beneficial impact of PIA in the setting of primary PCI regarding infarct size and prognosis. Possible pathophysiologic mechanisms and potential impact on primary PCI outcomes should be clarified in further larger calibre studies.