ATLAS ACS 2 - TIMI 51 is a phase III, multicenter, randomized, double-blind, placebo-controlled clinical trial evaluating an oral, direct factor Xa inhibitor (rivaroxaban) in subjects following an acute coronary syndrome.  Subjects are to receive low-dose aspirin therapy (75 to 100 mg/day), and enrollment will be stratified based upon the intent of the investigator to administer a thienopyridine [Stratum 1 (aspirin only) and Stratum 2 (aspirin plus a thienopyridine)].  Two different doses of rivaroxaban will be tested: 2.5 mg twice a day and 5.0 mg twice a day.