The pulmonary arterial pressure of a child with severe pulmonary arterial hypertension immediately normalized while breathing nitric oxide during heart catheterization at 8 years of age. Her acute pulmonary vascular response to nitric oxide has persisted throughout her life. Her acute response to other medications has been similar to her long-term response to medications in the same class. Acute vasodilator testing with inhaled nitric oxide and other medications may be an opportunity to refine study design and advance precision care for patients with pulmonary hypertension.