Cardiopulmonary exercise testing is a useful noninvasive tool to assess physiological changes associated with exercise. Developing noninvasive methods to assess the severity of cardiopulmonary disorders, as well as the response to therapeutic interventions, is useful in conditions, such as primary pulmonary hypertension, in which invasive procedures carry significant risks. The 6-minute walk test is a simple measure of exercise endurance. Exercise studies that measure both hemodynamic and ventilatory responses provide additional information regarding the interaction of the circulatory and pulmonary systems. Subtle changes in exercise capacity may suggest deterioration prior to clinical manifestations. This may lead to an earlier reevaluation, including repeat cardiac catheterization, and subsequently changes in medical and/or surgical therapy.