Subjects will be over the age of 21 years. The patients will be enrolled from sites within a reasonable travel distance from the greater Washington area and will receive their exercise training at Inova Fairfax Hospital or at the National Institutes of Health (NIH) main campus. Exercise-based rehabilitation is already common for patients who have PH at the Inova Fairfax Hospital. Their pulmonary rehabilitation program is well established, and their staff is experienced in providing exercise therapy for patients with PH and advanced lung diseases. The Rehabilitation Medicine Department (RMD) at The NIH Clinical Center has established a pulmonary rehabilitation program for this protocol as well as to provide rehabilitation services for NIH clinic patients.