Increased levels of pSTAT3 (Tyr705) were found in SMCs in PAH (Courboulin et al., 2011), and in alveolar hypoxia we found increased pulmonary level of pSTAT3 (Tyr705) protein localized to the muscle layer in pulmonary vessels by immunohistochemistry, indicating STAT3 as a mechanism of SMC proliferation in hypoxic pulmonary hypertension. This evidence concerns the gene STAT3 and pulmonary arterial hypertension.