Background: About 5% of patients with acute coronary syndrome (ACS) have had previously ischemic stroke (IS) or transitory ischemic attack (TIA). This is a high-risk population, with a high incidence of ischemic events, and also of bleeding events. While the high ischemic risk in this population is attributed to a higher prevalence of cardiovascular risk factors, their predisposition to bleeding events is not well understood. Hypothesis: The increased bleeding risk in ACS patients with history of cerebrovascular event may be justified by a low platelet activity. Methods: Unicentric, prospective, case-control study, which included approximately 100 post-ACS patients with history of IS/TIA previously to the acute coronary event (Case Group) and 100 patients without IS/TIA (Control group). The groups were matched for gender, age, and ACS type and year of occurrence. All patients were taking aspirin, and the main exclusion criteria were use of dual antiplatelet therapy, previous hemorrhagic stroke, severe renal dysfunction, thrombocytopenia or coagulopathy. Main analysis: Platelet aggregation was evaluated by 6 methods: VerifyNow Aspirin®, VerifyNow P2Y12®, PFA 100®, thrombelastography (ReoRox®), light transmission aggregometry with ADP (LTA ADP) and epinephrine (LTA EPI) as agonists. Additional analysis: genetic, HDL transport and inflammatory evaliation