Participants hospitalized with acute coronary syndrome (ACS)

anticipated to undergo percutaneous coronary intervention (PCI)

Participants provide signed informed consent form (ICF)

Participants weigh at least 60 kilograms (kg) at the time of screening

test negative for pregnancy at the time of enrollment based on a urine or serum pregnancy test

Have cardiogenic shock at the time of randomization

Have refractory ventricular arrhythmias

Have New York Heart Association (NYHA) Class IV congestive heart failure

Have systolic blood pressure greater than 180 mm Hg, or diastolic blood pressure greater than 100 mm Hg on more than 1 assessment at any time from participant presentation of ACS treatment to enrollment

Have systolic blood pressure greater than 180 mm Hg, or diastolic blood pressure greater than 100 mm Hg on more than 1 assessment at any time from participant presentation of ACS treatment to enrollment

Have received fibrin-specific fibrinolytic therapy less than 24 hours prior to randomization

Have active internal bleeding or history of bleeding diathesis

Have clinical findings associated with an increased risk of bleeding

Prior history of ischemic or hemorrhagic stroke

Intracranial neoplasm

arteriovenous malformation

aneurysm

Prior history of transient ischemic attack (TIA)

Have an International Normalized Ratio (INR) known to be greater than 1.5 at the time of evaluation

Have a platelet count of less than 100,000 per cubic millimeter (mm^3) at the time of evaluation

Have anemia [hemoglobin (Hgb) less than 10 grams per deciliter (g/dL)] at the time of evaluation

Have received 1 or more doses of a thienopyridine or other adenosine diphosphate (ADP) receptor inhibitor within 10 days prior to screening

Have been administered glycoprotein IIb/IIIa (GPIIb/IIIa) inhibitor within the past 7 days or planned use of a GPIIb/IIIa inhibitor during PCI

Are receiving or will receive oral anticoagulation or other antiplatelet therapy, other than aspirin (ASA), which cannot be safely discontinued for the duration of the study.

Are receiving daily treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX2) inhibitors that cannot be discontinued during the study

Are women who are known to be pregnant

Breastfeeding

Have known severe hepatic dysfunction (that is, with cirrhosis or portal hypertension)

Have a history of intolerance or allergy to aspirin or approved thienopyridines (ticlopidine, clopidogrel or prasugrel)