Inclusion Criteria:

• Patient >18 years of age.
• Patient presents with acute coronary syndrome (ACS) or stable coronary artery disease (CAD).
• Patient is eligible for PCI.
• Patient is willing and able to provide informed written consent.

Exclusion Criteria:

• Patient not able to receive 12 months of dual anti-platelet therapy.
• Failure of index PCI.
• Patient or physician refusal to enroll in the study.
• Patient with known CYP2C19 genotype prior to randomization.
• Planned revascularization of any vessel within 30 days post-index procedure and/or of the target vessel(s) within 12 months post-procedure.
• Anticipated discontinuation of clopidogrel or ticagrelor within the 12 month follow up period, example for elective surgery.
• Serum creatinine > 2.5 mg/dL within 7 days of index procedure
• Platelet count < 80,000 or > 700,000 cells/mm^3, or white blood cell count < 3,000 cells/mm^3 if persistent (at least 2 abnormal values) within 7 days prior to index procedure.
• History of intracranial hemorrhage.
• Known hypersensitivity to clopidogrel or ticagrelor or any of its components.
• Patient is participating in an investigational drug or device clinical trial that has not reached its primary endpoint.
• Patient previously enrolled in this study.
• Patient is pregnant, lactating, or planning to become pregnant within 12 months.
• Patient has received an organ transplant or is on a waiting list for an organ transplant.
• Patient is receiving or scheduled to receive chemotherapy within 30 days before or after the procedure.
• Patient is receiving immunosuppressive therapy or has known immunosuppressive or autoimmune disease (e.g., human immunodeficiency virus, systemic lupus erythematous, etc.).
• Patient is receiving chronic oral anticoagulation therapy (i.e., vitamin K antagonist, direct thrombin inhibitor, Factor Xa inhibitor).
• Concomitant use of simvastatin/lovastatin > 40 mg qd.
• Concomitant use of potent CYP3A4 inhibitors (atazanavir, clarithromycin, indinavir, itraconazole, ketoconazole, nefazodone, nelfinavir, ritonavir, saquinavir, telithromycin and voriconazole) or inducers (carbamazepine, dexamethasone, phenobarbital, phenytoin, rifampin, and rifapentine).
• Non-cardiac condition limiting life expectancy to less than one year, per physician judgment (e.g., cancer)
• Known history of severe hepatic impairment.
• Patient has a history of bleeding diathesis or coagulopathy or will refuse blood transfusions.
• Patient has an active pathological bleeding, such as active gastrointestinal (GI) bleeding
• Inability to take aspirin at a dosage of 100 mg or less.
• Current substance abuse (e.g., alcohol, cocaine, heroin, etc.).