Definitions and epidemiology Pulmonary hypertension is defined as resting mean pulmonary artery pressure of ≥ 25 mm Hg. Pulmonary hypertension is not in itself a diagnosis, but solely a hemodynamic state characterized by resting mean pulmonary artery pressure (PAPm) of ≥ 25 mm Hg. The term pulmonary arterial hypertension describes a subgroup that is hemodynamically distinguished by precapillary pulmonary hypertension with elevated pulmonary vascular resistance (PVR), i.e., PAPm ≥ 25 mm Hg with normal pulmonary arterial wedge pressure (PAWP) ≤ 15 mm Hg and PVR >240 dyn × s × cm-5 (1, 2). For a diagnosis of pulmonary arterial hypertension,