Prasugrel/Clopidogrel Maintenance Dose Washout Study

Inclusion Criteria: * Male or female subjects \>/= 18 years and \<75 years of age * Weight \>/= 60 kg * On aspirin therapy (81 mg to 325 mg daily) at the time of screening and able to maintain a consistent aspirin dosing regimen from the baseline visit through the final study visit * Subjects who do not have contraindications for a thienopyridine (ie, prasugrel, clopidogrel or ticlopidine), and have a history of stable atherosclerosis represented by Coronary Artery disease, defined as any of the following: * chronic stable angina * Prior history of acute coronary syndrome (\>/= 30 days before screening) including unstable angina or acute myocardial infarction (ST elevation Myocardial Infarction \[STEMI\] or non-ST elevation Myocardial Infarction \[NSTEMI\]), not currently prescribed or currently on thienopyridine therapy; * Previous coronary revascularization including percutaneous transluminal coronary angioplasty (PTCA), stent, or coronary artery bypass grafting (CABG) coronary artery disease (\>/= 50% obstruction) in at least one coronary vessel after angiography * Female subjects who meet one of the following: * Women of childbearing potential with a negative serum pregnancy test at screening who are not breast feeding, do not plan to become pregnant during the study, and agree to use an approved method of birth control during the study. Approved methods of birth control are oral, path, injectable or implantable hormonal contraception, intrauterine device, diaphragm plus spermicide, or female condom plus spermicide. Abstinence, partner's use of condoms, and partner's vasectomy are NOT acceptable methods of contraception. * Women who have been postmenopausal for at least 1 year or have had a hysterectomy, bilateral salpingo-oophorectomy, or tubal ligation at least 6 months prior to signing the informed consent form. * Subjects with a competent mental condition to provide written informed consent before entering the study. Exclusion Criteria: * Any other formal indication for the use of a thienopyridine. * Subjects with a history of refractory ventricular arrhythmias. * Subjects with a history of an implantable defibrillator device. * Subjects with a history or evidence of congestive heart failure (New York Heart Association \[NYHA\] Class III or above) within 6 months prior to screening. * Subjects with significant hypertension (systolic blood pressure \>180 mmHg or diastolic blood pressure \>110 mmHg) at either the time of screening or baseline assessment. * Bleeding Risk Exclusion Criteria: * Any known contraindication to treatment with an anticoagulant or antiplatelet agent * Prior history or clinical suspicion of cerebral vascular malformations, intracranial tumor, transient ischemic attack (TIA), or stroke, or recent history (within 3 months) of head trauma * Prior history or presence of significant bleeding disorders (eg, hematemesis, melena, severe or recurrent epistaxis, hemoptysis, hematuria, or intraocular bleeding) * History (within the last 5 years) or presence of gastric ulcers. Previous history of duodenal ulcer is acceptable but must have been successfully surgically or medically treated with no further evidence of disease in the past 6 months (from screening). * Prior history of abnormal bleeding tendency (ie, prolonged bleeding on dental extraction, tonsillectomy, or previous surgical procedure) * Known prior history of thrombocytopenia (platelet count \< 100,000/mm³) or thrombocytosis (platelet count \> 500,000/mm³) or recent history (within six months) of hemoglobin \< 10 mg/dL * Clinically significant out of range values for prothrombin time, activated partial thromboplastin time (aPTT), platelet count, or hemoglobin at screening, in the investigator's opinion * History of major surgery, severe trauma, fracture, or organ biopsy within 3 months prior to enrollment * Prior/Concomitant Therapy Exclusion Criteria: * Subjects taking prasugrel, clopidogrel, ticlopidine, cilostazol, dipyridamole, warfarin, heparin, direct thrombin inhibitors, or glycoprotein IIB/IIIa inhibitors =10 days prior to screening or during study participation * The use (or planned use) of fibrinolytic agents within 30 days before screening or during study participation * Subjects receiving treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX-2) inhibitors exceeding 3 doses per week * Subjects receiving proton pump inhibitors (PPIs), eg, (lansoprazole, esomeprazole, omeprazole, pantoprazole, or rabeprazole) =10 days prior to screening or during study participation * General Exclusion Criteria: * Investigator site personnel directly affiliated with the study or immediate family of investigator site personnel directly affiliated with the study. Immediate family is defined as a spouse, parent, child, or sibling, whether biological or legally adopted * Daiichi Sankyo or Eli Lilly employees * Currently enrolled in, or discontinued within the last 30 days prior to baseline from, a clinical study involving an off-label use of an investigational drug or device, or concurrently enrolled in a non-observational clinical study or any other type of medical research judged not to be scientifically or medically compatible with this study * Have previously completed or withdrawn from this study * Women who are known to be pregnant and/or who receive a positive serum pregnancy test result, who have given birth within the past 90 days, and/or who are breastfeeding * Results of clinical laboratory tests at the time of screening that are judged to be clinically significant for the subject, as determined by the investigator * Known allergies or intolerance to aspirin and/or thienopyridines (prasugrel, clopidogrel, or ticlopidine) * Evidence of significant active neuropsychiatric disease, alcohol abuse or drug abuse, in the investigator's opinion * Evidence of active hepatic disease, or any of the following; positive human immunodeficiency virus (HIV) antibodies, positive hepatitis C antibody, positive hepatitis B surface antigen; serum alanine transaminase (ALT), aspartate transaminase (AST), or gamma-glutamyltransferase (GGT) \>/= 3 times the upper limit of normal (ULN) laboratory reference range; or bilirubin \>/= 2 times the ULN of laboratory reference range at screening * Subjects who are unreliable and unwilling to make themselves available for the duration of the study and who will not abide by the research unit policy and procedure and study restrictions * Subjects who have had an angiogram \</= 7 days before randomization