The purpose of this study is to compare the response to aspirin in the acute phase with the late phase of an acute coronary syndrome.

The purpose of this study is to compare, in the same population, the response to aspirin in the initial phase (first 48 hours) with the late phase (after 3 months of discharge)of a non ST elevation acute coronary syndrome (angina or acute myocardial infarction).

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

70 patients diagnosed with non ST acute coronary syndrome (unstable angina and myocardial infarction without ST elevation), with up to 48 hours of evolution from the onset of symptoms.