Chronic thromboembolic pulmonary hypertension (CTEPH) is a form of pulmonary hypertension related to thromboembolic occlusion of the pulmonary vasculature. Most patients have a history of pulmonary embolism and develop symptoms despite appropriate anticoagulation, but as many as one-third of patients with the disease have no known history of acute venous thromboembolism. Therefore, lack of documented history of venous thromboembolism does not rule out chronic thromboembolic pulmonary hypertension.