Inclusion criteria were as follows: 1. >18 years of age, 2. Proven pre-capillary pulmonary hypertension as determined by RHC with an mPAP of ≥25 mm Hg in combination with pulmonary artery wedge pressure (PAWP) of ≤15 mm Hg, 3. Clinical classification into WHO groups I or IV following current guidelines35, and 4. Determination of fibrinogen plasma concentrations at time of catheterisation (within 3 days around the procedure). In all patients, lung ventilation and perfusion scintigraphy was used in addition to thoracic computed tomography.