 Chronic thrombo-embolic pulmonary hypertension CTEPH is thought to represent the consequence of failure of thrombus resolution after the establishment of thrombosis within the elastic pulmonary arteries. Thrombotic material becomes fibrosed, with occlusive vascular remodeling and the development of a secondary small vessel arteriopathy, termed the two-compartment model. This results in an increase in pressure and vascular resistance in the pulmonary vasculature and leads eventually to right heart failure. 