In this study, we elucidated the role of miR-223 in pulmonary vascular responses to hypoxia in vitro and in vivo, and identified a RhoB/ myosin light chain-2 (MCL2)-dependent role of miR-223 in PASMC and its clinical importance as a potential biomarker for the diagnosis of pulmonary arterial hypertension associated with congenital heart disease (CHD-PAH). The gene discussed is RHOB; the disease is pulmonary arterial hypertension.