ACVRL1 and pulmonary arterial hypertension: ;Bmp9−/− mice and its inhibition in C57BL/6 mice using neutralising anti-BMP9 antibodies substantially prevent against chronic hypoxia-induced pulmonary hypertension.The BMP9/BMP10 ligand trap ALK1 ECD administered in monocrotaline or Sugen/Hypoxia (SuHx) rats substantially attenuates proliferation of pulmonary vascular cells, inflammatory cell infiltration, and regresses established pulmonary hypertension in rats.