Despite treatment with aspirin a large number of patients suffer a myocardial infarction. It has been speculated that these patients might be "resistant" to aspirin, and studies have indicated that this phenomenon is related to a less favourable prognosis. At present, no international consensus exists on how to measure "aspirin resistance". The purpose of this study is to compare different methods for detecting "aspirin resistance". A classic but cumbersome way of evaluating platelet function will be compared to newer, easy-handling point-of-care tests. We hypothesize that one or more point-of-care tests will prove to be superior to the classic platelet function test in detecting aspirin resistance.