Ticagrelor is a new, reversible binding, anti-platelet medication. Anti-platelet medications work to prevent the formation of blood clots. Ticagrelor is being developed as a treatment for patients with acute coronary syndrome (ACS). ACS is a term that is used to describe both heart attacks in progress or the imminent threat of a heart attack. ACS is usually caused by the formation of a blood clot in an artery that partially or totally blocks the blood supply to a portion of the heart muscle. Ticagrelor will be compared with clopidogrel to determine which drug, when either is used in conjunction with aspirin, is better at reducing deaths from vascular causes, future heart attacks and/or strokes in patients with ACS.