Variables to be included. In all patients: a) date of onset of symptoms, b) medical history, c) personal and family history, c) treatment at enrollment, d) physical examination, d) WHO function class, e) six-minute walk distance, f) ECG, g) chest x-ray, h) echocardiogram, i) pulmonary function tests, j) V/Q lung scan and or pulmonary angiography, and/or pulmonary angiotomography k) right heart catheterization, and whenever possible indicated acute vasodilator challenge 11, 12, l) biomarkers: troponin I (TnI), brain natriuretic peptide (BNP), D - dimer (DD), INR, n) current treatment, o) in-hospital and follow - up outcome, p) MACE.