The pulmonary endothelium controls vasodilator/constrictor balance as well as vascular permeability and regulates the local balance between pro‐ and anti‐inflammatory mediators, anti‐coagulant and anti‐adhesive properties and cell proliferation.21 Vasomotor tone is controlled by the balance between vasodilators such as nitric oxide and prostacyclin and vasoconstrictors such as ET‐1.21 This balance is lost in PAH patients with increased ET‐1 release and reduced nitric oxide and prostacyclin production and current therapies are aimed at countering this imbalance. This evidence concerns the gene EDN1 and pulmonary arterial hypertension.