Patients seen in the Emergency Department, in-patient wards, out-patient clinics or anticoagulation clinics.

Inclusion Criteria:

1. First episode of acute symptomatic PE that was objectively diagnosed* within last 10 days
2. Treated with anticoagulants

3. ≥ 18 years old

   • PE will be diagnosed if there is a high probability V/Q scan (as per PIOPED Study criteria 66), an intraluminal filling defect in segmental or larger vessels on CTPA or a constant intraluminal filling defect or abrupt cut-off of vessels greater than 2.5 mm diameter on pulmonary angiography 8,10. Patients with non-definitive test results (e.g. low or intermediate probability V/Q scan, subsegmental PE on CTPA (~5% of PE patients 12) will not be included in order to have a strictly defined population of patients with definite PE.

Exclusion Criteria:

1. Contraindication or unable to perform CPET or 6MWT (amputated or paralyzed limb(s), severe lower extremity arthritis, preexisting cardiopulmonary condition precluding exercise including unstable angina or myocardial infarction in last 6 weeks, uncontrolled hypertension, serious cardiac dysrhythmia on resting EKG [severe bradycardia or tachycardia, sick sinus syndrome or multifocal premature ventricular contractions] and syncope)
2. Contraindication to CTPA (allergy to iodinated contrast, CrCl or eGFR < 30 ml/min)
3. Severe comorbidity (congestive heart failure [LVEF < 35%], severe COPD or restrictive lung disease [FEV1<50%, chronic need for oxygen therapy])
4. Previous DVT (as ~40% of patients with proximal DVT have asymptomatic PE on lung imaging 67)
5. Life expectancy < 1 year (e.g. active or terminal cancer, end-stage cardiac or respiratory disease).
6. Pregnancy
7. Unable to read questionnaire in English or French
8. Unable to return to study centre for required follow-up visits
9. Unable or unwilling to provide written informed consent