Study to Assess the Safety, Pharmacokinetics/Dynamics of DS-1040b in Subjects With Acute Submassive Pulmonary Embolism

Inclusion Criteria: * Male or female subjects, age 18 to 75 years admitted to hospital with a clinical diagnosis of acute pulmonary embolism (PE) categorized as low risk or intermediate-risk or submassive PE and for whom catheter-based therapy is not planned; * Subjects must have a computed tomography angiography (CTA) scan confirming the PE diagnosis and with at least one measurable index lesion in a segmental or larger pulmonary artery prior to randomization; * Subjects should be in otherwise satisfactory health in the opinion of the Investigator; * Subjects must be able to provide written informed consent. Exclusion Criteria: * Subjects with acute PE categorized as high-risk or massive, or who are hemodynamically unstable, evidenced by a heart rate \> 120 /min and a systolic blood pressure (SBP) of \< 90 mmHg for more than 15 consecutive minutes or a drop in SBP of \> 40 mmHg since presentation; * Subjects for whom use of a thrombolytic, either systemic or via catheter, is planned; * Subjects with PE lesions only in the sub-segmental or smaller arteries; * Subjects receiving any vitamin K antagonists (VKAs) prior to randomization or receiving more than 36 hours treatment with low molecular weight (LMW) Heparin in therapeutic doses prior to randomization; * Subjects who had a prior intracranial hemorrhage, known arteriovenous malformation or aneurysm, head trauma, or evidence of active bleeding; * Subjects who within 48 hours of randomization have used an anti-Factor IIa agent such as dabigatran or an anti-FXa agent such as rivaroxaban, apixaban, or edoxaban; * Subjects who within 21 days prior to randomization have had gastrointestinal or genitourinary bleeding; * Subjects who within 14 days prior to randomization have had major surgery or a lumbar puncture (or epidural steroid injection); * Subjects with diagnosed active liver disease or with elevation of liver enzymes/bilirubin.