Inclusion Criteria:

1)　Patients who consent for study participation and submit written informed consent with free will by patient or legally authorized representative.

2)　Patients aged between 20 years or above and under 75 years old at the time of obtaining informed consent.

3)　Patients with acute pulmonary embolism within 5 days after the onset.

4)　Patients with acute pulmonary embolism with hemodynamic instability and fulfill all of the following 4 items:

1. Confirmed to have thrombi, emboli, or disorders in pulmonary circulation detected by pulmonary angiography or computed tomography.

2. Confirmed to have any of the following right ventricular overloads by echocardiography:

   i) Dilation of right ventricular cavity or hypokinesis in ventricular wall

   ii) Floating thrombi in pulmonary artery and right heart

   iii) Paradoxical motion in the interventricular septum

   iv) Disparity of tricuspid regurgitation pressure

   v) Loss of inrespiratory changes of inferior vena cava in diameter

   vi) Enlargement of pulmonary artery

3. Mean pulmonary arterial pressure (PAP) is 20 mmHg or above
4. PaO2 is 65 mmHg or below (confirmed by blood gas analysis)

Exclusion Criteria:

1. Patients with concurrent hemorrhage (e.g., gastrointestinal bleeding, urinary tract bleeding, retroperitoneal bleeding, intracranial bleeding, or hemoptysis).
2. Patients who underwent intracranial or spinal operation or injury within 2 months prior to study treatment.
3. Patients with intracranial tumor, arteriovenous malformation, or aneurysm
4. Patients with hemorrhagic diathesis (e.g., vascular purpura, thrombocytopenia, hemophilia)　
5. Patients with hypertension of systolic blood pressure >=180 mmHg or diastolic pressure >= 110 mmHg.
6. Patients with a history of cerebrovascular disorder (e.g., cerebral infarction, intracerebral hemorrhage).
7. Patients with severe hepatic disorder (e.g., cirrhosis, severe hepatitis) or severe renal disorder (e.g., renal failure).
8. Patients received thrombolytic drug (t-PA or urokinase) within 7 days prior to study treatment.
9. Patients with pulmonary cardiac arrest (CPA).
10. Patients with a history of hypersensitivity to monteplase or protein preparations.
11. Pregnant women, women suspected of being pregnant, women who desire to become pregnant during a period between obtaining informed consent to the final observation, or lactating women.
12. Patients who are judged to be ineligible for study entry by the investigator or subinvestigator.