Rationale: Mechanisms that impair angiogenesis in neonatal pulmonary hypertension (PPHN) are poorly understood. Objective: To determine if PPHN alters fetal pulmonary artery endothelial cell (PAEC) phenotype and impairs growth and angiogenesis in vitro, and if altered VEGF-NO signaling contributes to this abnormal phenotype. Methods: Proximal PAECs were harvested from fetal sheep that had undergone partial ligation of the ductus arteriosus in utero (PPHN) and age-matched controls. Growth and tube formation ± VEGF and NO stimulation and inhibition were studied in normal and PPHN PAECs. Western blot analysis was performed for VEGF, VEGF receptor-2 (VEGFR-2) and eNOS protein content. NO production with VEGF administration was measured in normal and PPHN PAECs. Results: PPHN PAECs demonstrate decreased growth and tube formation in vitro VEGF and eNOS protein expression were decreased in PPHN PAECs, while VEGF-R2 protein expression was not different. VEGF and NO increased PPHN PAEC growth and tube formation to values achieved in normal PAECs. VEGF inhibition decreased growth and tube formation in normal and PPHN PAECs. NOS inhibition decreased growth in normal and PPHN PAECs, but tube formation was only reduced in normal PAECs. NO reversed the inhibitory effects of VEGF-R2 inhibition on tube formation in normal and PPHN PAECs. VEGF increased NO production in normal and PPHN PAECs. Conclusions: PPHN in utero causes sustained impairment of PAEC phenotype in vitro, with reduced PAEC growth and tube formation and down-regulation of VEGF and eNOS protein. VEGF and NO enhanced growth and tube formation of PPHN PAECs.