In patients over age 65, cardiovascular disease accounts for the largest percentage of deaths, hospital days, doctor visits, and overall health care expenditures. In addition, heart failure is the most common discharge diagnosis in the elderly. Heart failure can be defined as a state in which cardiac output is insufficient to meet metabolic demands. This is most frequently manifested by symptoms of fatigue and dyspnea. Inherent in this definition is that symptoms may be increased or only occur during times when metabolic demand is increased, such as during exercise. As such, exercise intolerance is a hallmark of the heart failure syndrome. Exercise intolerance correlates not only with disease severity and also with subsequent mortality. Exercise tolerance can be objectively quantified during maximal symptom limited standardized exercise protocols by analysis of exercise time, workload, METS (metabolic equivalents), and oxygen consumption (V02)' These measures have appropriately become accepted as standards for functional assessment in this disorder as well as outcome measures following therapeutic interventions in HF. P.A.R.I.S. is a randomized, attention-controlled, single-blind trial of supervised aerobic exercise training in older patients with heart failure. The primary outcome is exercise capacity and the main secondary outcome is quality of life. Mechanistic outcomes were also examined. In PARIS, which focused on cardiac mechanisms, there were HFPEF and HFREF patients studied in parallel. In PARIS-II, there were only HFPEF patients which focused on vascular mechanisms.