In order to test whether pro-angiogenic factors are decreased in pediatric PAH, we measured plasma VEGF-C concentrations, and found – similarly to IL-7–approximately 59% lower circulating VEGF-C levels in pediatric PAH vs. controls (SVC, PA, AAO; p < 0.001) that correlated negatively with the PVR/SVR ratio (r = −0.62, p = 0.0034; Figure 1B). Here, IL7 is linked to pulmonary arterial hypertension.