• The purpose of this study is to determine the level of inhibition of platelet activation of an approved thienopyridine(clopidogrel or prasugrel) and aspirin regimen in the setting of drug eluting coronary stent implantation.
• In subjects with high residual levels of platelet reactivity after receiving either a maintenance or loading dose of either clopidogrel or prasugrel, a cross over of thienopyridine treatment to the alternate medication will occur.
• The study tests the hypothesis that adequate platelet inhibition will occur in subjects who have high levels of platelet reactivity and are subsequently switched from clopidogrel to prasugrel(loading or maintenance dose) without increased episodes of bleeding or MACE events at discharge and 30 days post Percutaneous Coronary Intervention (PCI).

Inclusion Criteria:

• Subject presenting for clinically indicated PCI with implantation of at least one drug-eluting stent.
• No planned use of Glycoprotein IIb/IIIa inhibitors during PCI procedure.
• Subject must be taking aspirin or enteric coated aspirin 81 mg-325 mg daily.
• Willing to participate and sign an informed consent.

Exclusion Criteria:

• Subject older than 75 years of age.
• Subject weight is 60 kg or less.
• Subject who have received intravenous eptifibatide or tirofiban within 48 hours prior to PCI or abciximab within 14 days before or during PCI.
• Subject taking warfarin or with clinical indication to resume warfarin post PCI for any indication.
• Subject currently requiring daily treatment with NSAID or COX2 inhibitors.
• Subject with a known platelet disorder.
• Subject with known active pathological bleeding or heightened risk of bleeding including but not limited to: gastrointestinal bleeding within 6 months, recent surgery or trauma.
• Subject with a history of a stroke or TIA
• Subject with pre-PCI hematocrit or platelet count outside the ranges validated for Verify Now P2Y12 test (33-52% and 119.000-502.000/μL, respectively).
• Subject with a history of hepatic impairment
• Subject with known NYHA Class III or greater for heart failure.
• Inability of subject to provide informed consent.
• Subject with known hypersensitivity or contraindication to clopidogrel, prasugrel or ASA, which would result in inability of patient to adhere to trial protocol.
• Presence of valvular heart disease left main coronary artery stenosis or urgent need for CABG.