We to measure the serum levels of hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) in patients diagnosed with connective tissue disease (CTD)-associated pulmonary arterial hypertension (PAH) (CTD-PAH) and to analyze their clinical implications. The gene discussed is VEGFA; the disease is pulmonary arterial hypertension.