 - Patients must be diagnosed with CTEPH within 6 months of being considered for study eligibility signing of consent to participate. The date of diagnosis will be defined as when both hemodynamic criteria have been met and chronic thromboembolic disease is confirmed to be the cause of the pulmonary hypertension by an abnormal VQ scan and the presence of chronic thromboembolic disease on CTA, MRA or pulmonary angiography. Hemodynamic and radiologic criteria can be met at separate time points; the most recently met criteria time point will be defined as the date of diagnosis. 