The purpose of this study is to estimate the risk of bleeding with rivaroxaban, compared with acetylsalicylic acid (ASA), in addition to a single antiplatelet/ platelet adenosine diphosphate P2Y12 receptor antagonist (P2Y12 inhibitor agent: clopidogrel or ticagrelor), in participants with a recent acute coronary syndrome (ACS: including ST segment elevation myocardial infarction [STEMI] and non-ST-segment elevation acute coronary syndrome [NSTE-ACS]).

This is a prospective, randomized (the study drug is assigned by chance), double-blind (neither physician nor participant knows the treatment that the participant receives), active-controlled (study in which the experimental treatment or procedure is compared to a standard treatment or procedure), parallel group (each group of participants will be treated at the same time), multicenter (when more than one hospital or medical school team work on a medical research study) study in participants with a recent ACS (STEMI or NSTE-ACS). All the eligible participants receiving background treatment of ASA plus clopidogrel (Stratum 1) or ASA plus ticagrelor (Stratum 2) will be randomly assigned to either receive ASA or rivaroxaban on background of P2Y12 receptor antagonists treatment. This study will include 3 phases: Screening Phase (up to 10 days, before study start on Day 1), Double-blind Treatment Phase (up to either 180 days after randomization of the last enrolled participant in the study or Day 360, whichever occurs earlier), and Follow-up Phase (up to 30 days). Participants' safety will be monitored throughout the study.

Inclusion Criteria:

• Participants, 18 years or older, must have symptoms suggestive of acute coronary syndrome (ACS) (angina, or symptoms thought to be equivalent) within 48 hours of hospital presentation, or developed ACS while being hospitalized, and has a diagnosis of: a) ST segment elevation myocardial infarction (STEMI); b) non-ST-segment elevation acute coronary syndrome (NSTE-ACS). However, participant who is 54 years of age or younger must also have either diabetes mellitus or a history of a prior myocardial infarction (MI), in addition to the presenting ACS event
• Participant must be randomized within the screening window of 10 days after hospital admission for the index ACS event. Participant should have received acute phase treatment for the index ACS, such as intravenous anticoagulant or antiplatelet, and are receiving maintenance dual antiplatelet therapy (DAPT) with either clopidogrel plus acetyl salicylic acid (ASA), or ticagrelor plus ASA, with the intent to continue the treatment with a platelet adenosine diphosphate P2Y12 receptor antagonist (P2Y12 inhibitor) after randomization
• Participants must agree to provide a pharmacogenomics deoxyribonucleic acid (DNA) sample

Exclusion Criteria:

• Participant has any conditions that, in the opinion of the investigator, contraindicates anticoagulant therapy or would have an unacceptable risk
• Participant with a prior stroke of any etiology or transient ischemic attack (TIA)
• Participant who received thrombolytic therapy as treatment for the index ACS event cannot be enrolled in the ticagrelor stratum
• Participant has anticipated need for chronic administration of omeprazole or esomeprazole concomitantly with clopidogrel
• Participant has known allergy or intolerance to ASA or rivaroxaban