Right heart catheterization Invasive hemodynamic assessment with right heart catheterization is requested to confirm the diagnosis of PH showing a resting mPAP of ≥25 mmHg and a normal PCWP [2]. This value has been used for selecting patients in all RCTs and registries of PAH, however normal mPAP at rest is around of 14 mmHg, with an upper limit of normal of 20 mm Hg. The significance of a mean PAP between 21 and 24 mmHg is currently unclear. No definition of PH on exercise was currently adopted, because of the large variability of mPAP on exercise in healthy individuals. The assessment of PCWP may allow the distinction between precapillary (normal PCWP ≤15 mmHg) and postcapillary PH (PCWP >15 mm Hg). In post-capillary PH, the last guidelines from the 4th World Symposium (Dana Point) proposed a dichotomy between "passive" and "reactive" (out-of-proportion) post-capillary PH based on transpulmonary pressure gradient (mPAP–PCWP, respectively ≤ or > 12 mm Hg). Indeed, there is no clear consensus on this definition and the future recommendations arising from the last World Symposium on PH (Nice, 2013) should propose new definition to define these two entities. Measurement values obtained by RHC are PAP (diastolic, mean and systolic), right atrial pressure (RAP), PCWP, right ventricular pressure and cardiac output (CO) preferably by the thermodilution method. In contrast to the thermodilution method, the Fick method is mandatory in patients with suspected CHD. In experienced centres, RHC procedures have low morbidity and mortality rates [195]. Elevated mean right atrial pressure reduced CO and mixed venous oxygen saturation (SVO2) are related to the prognosis of PAH patients.