In this study, STEMI patients undergoing PPCI, in whom epicardial reperfusion was achieved (TIMI-3 flow) by wire crossing or by balloon angioplasty or aspiration thrombectomy, will be randomised to immediate and delayed stenting groups. Delayed stenting will be performed at the time when coronary auto regulation was recovered which is going to be determined based on the continuous intracoronary hemodynamic monitoring after reperfusion.