Downstream Versus Upstream Strategy for the Administration of P2Y12 Receptor Blockers

Inclusion Criteria: * Age ≥ 18 and \< 85 * Non ST elevated acute coronary syndrome (unstable angina, non ST elevated myocardial infarction), with an onset of symptoms during the previous 24 hours. * An initial invasive strategy is chosen (the patient is expected to undergo coronary angiography within 72 h from admission). * Subject is able to start therapy with a new P2Y12 inhibitor (prasugrel or ticagrelor) OR is on a maintenance dose of clopidogrel or ticlopidine and is able to switch to a new P2Y12 inhibitor (prasugrel or ticagrelor). * Subject is able to verbally confirm understanding of risks and benefits of dual antiplatelet therapy in coronary acute syndromes and he/she or his/her legally authorized representative provides written informed consent prior to any Clinical Investigation related procedure, as approved by the appropriate Ethics Committee. * Patient agrees to comply with follow-up evaluations. Exclusion Criteria: * Known hypersensitivity/contraindication to aspirin, clopidogrel, prasugrel, ticagrelor, heparin or bivalirudin, or sensitivity to contrast media, which can't be adequately pre-medicated. * Platelet count \<100,000 cells/mm³ or \>700,000 cells/mm³, or a white blood cell (WBC) count \<3,000 cells/mm³ within 7 days prior to index procedure. * Shock. * Have severe hepatic impairment defined as Child Pugh Class C. * Pregnant or nursing subjects and those who plan pregnancy in the period up to 3 years following screening. (Female subjects of child-bearing potential must have a negative pregnancy test done within 28 days prior to enrollment). * Other medical illness (e.g., cancer or congestive heart failure) or known history of substance abuse (alcohol, cocaine, heroin etc.) as per physician judgment that may cause non-compliance with the protocol or confound the data interpretation or is associated with a limited life expectancy. * Subject is belonging to a vulnerable population (per investigator's judgment, e.g., subordinate hospital staff or sponsor staff) or subject unable to read or write. * Currently participating in investigational drug or device trial that has not completed the primary endpoint or that clinically interferes with current trial endpoints. Subject must agree not to participate in any other clinical investigation for a period of three years following the index procedure, including clinical trials of medication and invasive procedures. Questionnaire-based studies, or other studies that are non-invasive and do not require medication are allowed. * Prior history of hemorrhagic or ischemic stroke, a transient ischemic attack (TIA), or sub-arachnoid hemorrhage. * History of intracranial neoplasm, arterovenous malformation, or aneurysm. * Have received fibrinolytic therapy within 48 hours of entry or randomization into the study. * Have active pathological bleeding or history of bleeding diathesis. * Have clinical findings, in the judgment of the investigator, associated with an increased risk of bleeding. * Have had recent surgery (within 4 weeks of entry into the study) or are scheduled to undergo surgery within the next 2 months. * Have received a loading dose of a thienopyridine (ticlopidine, clopidogrel or prasugrel) or a maintenance dose of prasugrel or Ticlopidine or Ticagrelor within 7 days of entry into the study. * Are receiving a GPIIb/IIIa inhibitor (eptifibatide, tirofiban, or abciximab). * Are receiving warfarin or other coumarin derivatives. * Are receiving or will receive oral anticoagulation or other oral antiplatelet therapy (except aspirin \[ASA\]) that cannot be safely discontinued within the next 3 months. * Are receiving daily treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX2) inhibitors that cannot be discontinued or are anticipated to require \>2 weeks of daily treatment with NSAID or COX2 inhibitors during the study. * Concomitant therapy with a strong cytochrome P-4503A inhibitor or inducer.