Enduro™ is a portable, battery powered, noninvasive cardiac output device that was designed primarily to be used while a subject or patient is exercising. Enduro™ is unique in that it is the only device that can reliably and repeatedly provide cardiac output during exercise. A fundamental characteristic of patients with chronic heart failure is an impaired ability to increase cardiac output appropriately with exercise. Many patients are able to improve cardiac output after interventions; cardiac resynchronization therapy and exercise training are directly correlated with this. Quantifying cardiac output can therefore provide important information about these and other interventions. Recent studies have also demonstrated that this information is valuable in predicting outcomes in patients with cardiovascular disease.