Despite a large number of patients screened, very few met eligibility guidelines.

Subjects presenting with probable acute coronary syndromes scheduled for cardiac catheterization will be enrolled in this study. Consented subjects will be randomized to receive ticagrelor started with a loading dose immediately after enrollment versus receiving a loading dose of ticagrelor during cardiac catheterization after diagnostic angiography but prior to stenting. Optical coherence tomography (OCT) will be performed after stenting and the volume of thrombus within the new stent will be measured and compared between the groups.

Inclusion Criteria:

Patient Characteristics:

1. Males and non-pregnant females > or equal to 18 and < or equal to 79 years of age presenting with suspected acute coronary syndrome (unstable angina or NSTEMI)
2. Patients likely to be scheduled to undergo coronary angiography with possible percutaneous coronary intervention (PCI)

Lesion Characteristics on Diagnostic Coronary Angiography:

1. De novo lesions in native coronary arteries found by diagnostic coronary angiography
2. Angiographic stenosis <100%
3. Reference vessel diameter 2.5 mm - 4.0 mm by visual estimation

Exclusion Criteria:

Patient Specific Exclusion Criteria:

1. Subjects who are unable or unwilling to sign the informed consent form.
2. Subjects being treated with anti-platelet medications other than aspirin prior to diagnostic catheterization including glycoprotein IIb/IIIa inhibitors.
3. Subjects with serious co-morbid conditions that in judgment of the investigator preclude inclusion in this study
4. Subjects with NYHA class III or IV heart failure or known left ventricular ejection fraction < 30%.
5. Subjects with an ST elevation myocardial infarction.
6. Subjects with hemodynamic or electrical instability (including shock).
7. Subjects diagnosed with severe, non-catheter-related coronary artery spasm.
8. Subjects who are or may be pregnant.
9. Subjects with known allergies to contrast media.
10. Subjects with eGFR < 60 ml/min/1.73m2.
11. Subjects currently taking oral anticoagulants with an absolute contraindication to discontinuation of anticoagulation.
12. History of TIA or stroke < 6 months.
13. History of hemorrhagic stroke.
14. Hepatic insufficiency defined as liver cirrhosis, AST/ALT/Alkaline Phosphatase greater than 3 times the upper limit of normal or hyperbilirubinemia.
15. Cardiac catheterization scheduled within 4 hours of randomization or more then 72 hours after randomization.

Lesion Specific Exclusion Criteria. These exclusion criteria apply to the target lesion to be imaged by OCT.

1. Lesions located in the left main coronary artery
2. Lesions that are heavily calcified
3. Lesions where OCT cannot be performed due to technical difficulties
4. Other lesions that the investigator deems inappropriate for the procedure such as sites with excessive tortuosity or low flow by TIMI grade.
5. Lesions in saphenous vein grafts or arterial conduits.