Left Ventricular Assist Device (LVAD) Specialized Centers of Clinically Orientated Research (SCCOR) Coagulation - Acute Intrinsic Pathway Antagonist (IPA)

Inclusion Criteria: * Signed informed consent, release of medical information, and HIPAA forms * Age greater than or equal to 18 years * Male, postmenopausal female, or female who may become pregnant but is using adequate contraceptive precautions (defined as oral contraceptive, intrauterine devices, surgical contraception or a combination of a condom and a spermicide), with negative pregnancy test * Implanted with an FDA-approved LVAD (for BTT or DT indication, e.g. HeartMate® XVE) within 72 hours prior to randomization, and able to receive the first dose of study drug by 72 hours (+6 hours) post LVAD implantation * Post-op hemostasis adequate for starting low level anticoagulation (as assessed by surgeon) * Extubated and able to take oral medication Exclusion Criteria: * Evidence of active bleeding within 24 hours prior to randomization * History of a platelet disorder, including but not limited to thrombocytopenia and thrombasthenia * Thrombocytopenia with platelets \<80,000/ml within 48 hours prior to randomization * History of an inherited or acquired coagulation disorder * Hemoglobin \<8 g/dL (4.85 mmol/L) or hematocrit \<26% within 24 hours prior to randomization * Clinical indication for (or the intention to use) standard anticoagulation therapy at time of randomization (e.g., atrial fibrillation or DVT) * Intention to treat with more than 325 mg aspirin daily * Any clinical requirement or intention to treat with phenytoin, tolbutamide or warfarin post randomization * RVAD support at the time of randomization * Estimated glomerular filtration rate (GFR) ≤30 ml/min (by Cockcroft-Gault formula), or any form of dialysis within 48 hours prior to randomization * Evidence of intrinsic hepatic disease as defined as biopsy proven liver cirrhosis; or liver enzyme values (AST or ALT) that are \>3 times the upper limit of normal; or Total Bilirubin \>1.5 times the upper limit of normal (with the exception of Gilbert's Syndrome) within 3 days prior to randomization * Active systemic infection, in the judgment of the investigator, within 3 days prior to randomization * Stroke or transient ischemic attack (TIA) within 6 months prior to randomization * History of intracranial hemorrhage or gastrointestinal bleed within 3 months prior to randomization * Alzheimer's disease, or any other form of irreversible dementia * History of psychiatric disease (including drug or alcohol abuse) that may impair compliance with the study protocol * Pregnant or breastfeeding at time of randomization * Received investigational intervention within 30 days prior to randomization * Body weight \< 45 Kg