A vasodilator study is performed when the Pulmonary hypertension patient is undergoing a right heart catheterization. A vasodilator study evaluates the pulmonary arteries’ response to medications, such as adenosine, NO, or epoprostenol, that cause vasodilatation. While there is no definitive wording on what constitutes a positive vasoreactivity response, it is believed that MPAP > 40 mmHg while receiving a vasodilator is a positive response. The presence or absence of vasoreactivity of the pulmonary vasculature provides a diagnosis and guides treatment.