Evaluation of data from large registries identified a set of risk factors for CTEPH including ventriculo-atrial shunts, infected pacemaker leads, splenectomy, previous venous thromboembolism, thyroid hormone replacement therapy and a history of malignancy12. Although dysregulation of thrombosis and thrombolysis is observed in a subgroup of CTEPH patients3 this mechanism does not fully explain the pathophysiology. Important classical thromboembolic risk factors are lacking and in about 25% of the CTEPH patients APE occurred asymptomatically1. Hence, the mechanistic view of CTEPH as a consequence of central pulmonary vessel obstruction appears to be too simplistic1.