Inclusion

* 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

5.3 Exclusion

* 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/mm3, or white blood cell count \<3,000 cells/mm3 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.)