Residual Platelet Activity Despite Aspirin Utilization in Coronary Heart Disease

Inclusion Criteria: * Age ≥ 18 years * Confirmed diagnosis of acute coronary syndrome without ST segment elevation, in the first 48 hours after the onset of the clinical symptoms * Regular use of aspirin for at least seven days. Exclusion Criteria: * Previous use, in the last 7 days, of another antiplatelet agent than aspirin * Use of antivitamin K in the last 3 weeks * Hemoglobin \< 10g/dL and / or hematocrit \< 30% or \> 50%, platelets count \< 100.000/mm3 or \> 500.000/mm3, creatinine clearance \< 30 mL / minute * Killip class III or IV * Need for vasopressor or inotropic parenteral medication at inclusion in the study * Percutaneous coronary intervention within 30 days or CABG in the last 90 days prior to study entry * Current malignancy * Hematologic diseases * Refusal to sign the inform consent form * Unable to attend the second visit (follow-up) for any reason except for death