Inclusion Criteria:  patient admitted for STEMI within 24 hours from symptom onset pretreated with ticagrelor, aspirin and enoxaparin (according local protocol) successfully treated by primary PCI of a native coronary culprit lesion anatomy accessible to optical coherence tomography (OCT or OFDI)  Exclusion Criteria:  cardiogenic shock stent restenosis or thrombosis use of glycoprotein IIb/IIIa inhibitors before or during PCI known coagulation disease high bleeding risk (thrombocytopenia <100,000/dL, surgery <30 days, active bleeding) uncontrolled arterial hypertension (>180/110 mmHg) history of stroke (ischemic or hemorrhagic) or transient ischemic attack known severe renal insufficiency (eGFR <30 ml/min) oral anticoagulation