In addition to sustained increases in PDGF‐β and the TGF‐β1 pathway components, Nox‐4 and PAI‐1, we observed transient increases in VEGF, TPH‐1, and IL‐6, mediators associated with de‐regulated proliferation of activated microvascular endothelial cells and formation of plexiform lesions in primary PAH. This evidence concerns the gene NOX4 and pulmonary arterial hypertension.