Pulmonary vasodilator testing is performed during right-heart catheterization and involves a short-acting vasoactive agent such as adenosine, epoprostenol, or inhaled nitric oxide. The current definition of a normal (positive) response is a drop in mean pulmonary artery pressure of at least 10 mm Hg (or 20 percent) to below 40 mm Hg. [from HPO]