Pediatric pulmonary arterial hypertension (PAH) is a significant cause of morbidity and mortality. Acute vasodilatory reactivity (AVR) using right heart catheterization is a necessary component of a diagnostic PAH evaluation. The aim of this study was to non-invasively evaluate AVR hemodynamic changes in pediatric patients with PAH using 4D flow MRI. We have shown that post-iNO treatment in pediatric PAH patients, peak velocity and peak wall shear stress were increased. Future studies in larger cohorts of PAH pediatric patients are needed to comprehensively evaluate the effectiveness of non-invasive AVR in comparison to gold standard right heart catheterization.