Pulmonary Arterial Hypertension (PAH) is a syndrome in which the blood pressure in the pulmonary arteries and pulmonary arterioles (the blood vessels located proximal to the capillary bed, the site of oxygen exchange in the lungs) is elevated. This pre-capillary pulmonary artery pressure being elevated is essential, and by definition a mean pulmonary artery pressure greater than 20 mmHg as measured by a right heart catheterization is required for the diagnosis...