An initial assessment of platelet reactivity in response to the TRAP (thrombin receptor agonist), ADP and arachidonic acid (respectively, indicative of the response to clopidogrel and aspirin) will be performed with impedance aggregometry (Multiplate® analyzer system). Patients with a increased residual platelet reactivity to ADP test (AUC > 47) will receive a different antiplatelet therapy and will then be excluded from the study, the other will be randomized to 3 groups of treatment.