Apelin levels are downregulated in plasma or serum19,25 in PAECs26 and pulmonary microvascular endothelial cells27 from PAH patients and in RV of MCT-exposed rat.28 The expression of the apelin receptor was also reduced in RV of MCT rats.28 We have now shown for the first time that ELA is similarly reduced in pulmonary vessels of PAH patients and in the RV from 2 rodent models of PAH. This evidence concerns the gene APLN and pulmonary arterial hypertension.