The Effect of Reloading Prasugrel in a Patient Who Has Already Received a Loading Dose (LD) of Clopidogrel

Inclusion Criteria: 1. Patients age 18 or older, of both genders 2. Presenting with an ACS, defined as at least two of the following: Symptoms consistent with myocardial ischemia; ST segment elevation or depression of at least 1 mm in 2 or more contiguous leads on EKG; Cardiac troponin I level above the upper limit of normal. 3. An initial invasive strategy (e.g. early angiography) is planned. 4. No contraindications to prasugrel therapy. Exclusion Criteria: 1. Known allergies to aspirin, clopidogrel, or prasugrel. 2. Patient known to be pregnant or lactating. 3. Patient with known history of bleeding diathesis, or currently active bleeding. 4. Platelet count \<100,000/mm3 at the time of enrollment. 5. Hematocrit \<25% at the time of enrollment. 6. On warfarin therapy at the time of PCI, or patient likely to require warfarin therapy post-PCI. 7. Received fibrinolytics within the past 48 hours. 8. Received a glycoprotein IIb/IIIa inhibitor within the past 48 hours, or if a strategy for PCI involving a glycoprotein IIb/IIIa inhibitor is planned. 9. Taking maintenance thienopyridine therapy in the previous 7 days. 10. Known blood transfusion within the preceding 10 days. 11. Patients treated with non-steroidal anti-inflammatory drugs (NSAIDS) within the previous 5 days. 12. Patients with known chronic liver disease. 13. Age greater than 75 years. 14. Body weight less than 60 kg. 15. History of stroke or transient ischemic attack. 16. Surgery planned within 1 month. 17. Patient likely to require coronary artery bypass grafting. 18. Any significant medical condition that, in the investigator's opinion, may interfere with the patient's optimal participation in the study.