Method: Patients who meet the criteria of inclusion will be randomized to intra-coronary injection plus intravenous infusion of melatonin or placebo. The bolus will be given just after the opening of the vessel (TIMI ≥ 2) . Hs-Troponin T/I and CK-MB will be measured in a blood sample taken 1 hour, 6 hours, 24 hours, 48 hours, 72 hours and 96 hours after the PCI procedure. At day 4 after PCI, the patients will undergo MRI of the heart focusing on infarct size and area at risk.