Most patients with chronic thromboembolic pulmonary hypertension present late in the course of the disease.

Early natural history of the condition is not completely known.

Embolism can occur without symptoms and that symptomatic pulmonary embolism is often overlooked or misdiagnosed.

Patients with thromboembolic disease may remain asymptomatic for months or years.

Hemodynamic progression may involve recurrent thromboembolism or in situ pulmonary-artery thrombosis.

Hemodynamic progression appears to involve pulmonary vascular remodeling and the development of a hypertensive pulmonary arteriopathy.