Purpose: Identification of responders to acute vasoreactivity testing (AVT) is critical for prognostication and guiding medical therapies for children with pulmonary arterial hypertension (PAH). We sought to evaluate whether echocardiography is sensitive enough to detect changes in hemodynamics, and to accurately assess the acute response to AVT in pediatric pulmonary hypertension. Methods: Simultaneous echocardiography and invasive hemodynamics were obtained in 71 children with PAH at their baseline and maximal vasodilatory conditions. The change in echocardiographic parameters were used to predict AVT responder status as determined by two commonly used hemodynamic thresholds (Barst and Sitbon criteria). Results: There were strong positive correlations between invasive hemodynamics and echocardiographic markers of pulmonary hypertension. Between the baseline and AVT conditions, there were significant reductions in the tricuspid valve regurgitation velocity (TR Vmax), right ventricular systolic-to-diastolic ratio (S/D ratio), systolic and maximal eccentricity index (EIs and EIm). Barst criteria responders had more pronounced reductions in TR Vmax, S/D ratio, and EIm. A 22.5% decrease in TR Vmax, 48.2% in S/D ratio, 44.9% in EIs, and 29.0% in EIm were associated with positive Barst responder status. The degree of change in echocardiographic variables were not strongly associated with clinical outcomes. Conclusions: This is the first study to demonstrate that there are appreciable changes in echocardiographic markers of pulmonary hypertension during acute vasoreactivity testing in children. Changes in these markers could be utilized in the future as part of multiparametric predictive model to assess for AVT responder status, an independent predictor of long-term clinical outcomes.