If the genetic testing results confirm that the patient is a candidate for the interventional study, they will be contacted and asked to make an outpatient appointment to initiate the interventional study protocol. The therapeutic portion of this study will be a randomized, unblinded cross-over comparison of two clopidogrel dosing strategies. It is anticipated that all eligible patients will have continued their previous chronic clopidogrel therapy with standard dosing of 75 mg/day. Because all patients will be receiving chronic clopidogrel at the initiation of the intervention protocol, steady state levels should be present in all patients. Dose dependent inhibition of platelet aggregation can be seen two hours after a single oral dose of clopidogrel. Repeated doses of 75mg daily produce steady state inhibition between day 3 and day 7 of administration.