Inclusion Criteria:

Acute intermediate-risk PE, defined as:

• Intraluminal filling defect in segmental or larger vessels on computed tomography pulmonary angiography or high-probability ventilation/perfusion scan AND
• Evidence of right ventricular enlargement by computed tomography (RV to LV ratio >1) or echocardiography; and/or right ventricular dysfunction by transthoracic echocardiography. These imaging characteristics must be in the setting of acute PE rather than explained by a prior chronic condition.

Acute high-risk PE, defined as:

• Intraluminal filling defect in segmental or larger vessels on computed tomography pulmonary angiography or high-probability ventilation/perfusion scan AND
• Evidence of right ventricular enlargement by computed tomography (RV to LV ratio >1) or echocardiography; and/or right ventricular dysfunction by transthoracic echocardiography. These imaging characteristics must be in the setting of acute PE rather than explained by a prior chronic condition; AND
• Hypotension (systolic blood pressure < 90 mm Hg sustained for more than 15 minutes; or requiring vasopressors) or cardiogenic shock due to acute pulmonary embolism.

Exclusion Criteria:

• Inability to ambulate independently, which is necessary to perform 6MWD (may be self-reported or as deemed by physical therapy during inpatient evaluation).
• If patient requires supplemental oxygen during ambulation, this does not exclude patient from participation and will be noted during eCRF.
• Prior history of pulmonary embolism
• History of CTEPH or pulmonary arterial hypertension
• Unable to read a questionnaire in English
• Unable to return for baseline, 3- or 6-month follow-up visit
• Pregnancy-associated pulmonary embolism
• Life expectancy <1 year based on comorbidities
• Unable/unwilling to provide informed written consent