1. Platelet aggregation tests Aggregation studies will be performed within 3 hours after blood collection by Pascale Gaussem (INSERM U765, HEGP), as published elsewhere (10). Aggregation tests are performed on platelet-rich plasma adjusted to 250x109/L platelets using the following agonists: arachidonic acid 1.5 and 2 mmol/l (Helena biosciences Europe) to explore aspirin effect, Horm collagen 1 µg/ml to explore global platelet function (Nycomed Pharma) and ADP 10 and 20 µmol/l (Biopool) to explore clopidogrel effect.