This is a prospective, randomized, single-center, open platelet function study conducted in 60 STEMI patients. Subjects were randomly assigned to receive a loading dose (LD) of intravenous LA 450mg plus oral prasugrel 60mg/ticagrelor 180mg, or LD of aspirin 300mg plus prasugrel 60mg/ticagrelor 180mg orally. Platelet function was evaluated at baseline, 30 min, 1h, 4h, and 24h using multiple electrode aggregometry and vasodilator-stimulated phosphoprotein phosphorylation (VASP). The primary endpoint of the study is the inhibition of platelet aggregation after arachidonic acid (AA) 1.5mM at 30 min. Secondary endopoints are the inhibition of platelet aggregation after AA baseline and at 1h, 4h and 24h, and measurement of aggregation with other platelet test (ADP, collagen and VASP).