Patients belonging to Dana Point/WHO group II, III or V, patients with documented haematological disorders or significant coagulopathies including liver failure or elevated liver enzymes > 2.5-times upper normal limit were excluded. Anticoagulation was switched from coumadin to low-molecular-weight heparin prior to right heart catheterisation. PEA was offered to all patients with CTEPH who were deemed eligible candidates. During the same time frame a control group was generated from patients referred to the Hamburg centre with suspected PH that was eventually ruled out during the course of clinical workup (n = 11 patients). These cases were selected intentionally as control patients and should not be considered as healthy individuals as they reported symptoms severe enough to justify right heart catheterization in the first place.