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.