 Resistance to antiplatelet drugs aspirin, clopidogrel is a recognized phenomenon with a prevalence from 17 to 35. Resistance as detected by in vitro tests such as Multiple Electrode Aggregometry MEA has been shown to predict clinical therapy failure. Resistance can be caused by clinical, cellular and pharmacogenetic factors. Non compliance is suspected to be an important contributing factor. In this study, compliance will be assured with an electronical compliance monitoring system. Factors to non response will be identified to find plausible explanations when in vitro platelet aggregation inhibition is insufficient despite assured compliance. This study will help to disclose the relationship between compliance, biomarker and clinical outcome as well as to quantify the impact of non compliance to the resistance phenomenon as measured by MEA. 