Chronic heart failure (CHF) carries a mortality higher than many forms of cancer,1 as well as impairing quality of life and causing many acute hospital admissions.2 Despite the recent improvements in medical treatment, prevalence and mortality of CHF seem set to remain high.3

The convention of defining CHF in terms of symptoms, clinical signs, and findings on investigation has certain limitations. Firstly, although the principal symptoms—breathlessness and fatigue on exercise—may be pronounced, they overlap with those of patients with respiratory disease and can even be reported by normal subjects. Secondly, signs of fluid retention do not always persist with optimal medical treatment and when they are found they do not necessarily signify cardiac failure.4 Thirdly, while imaging investigations may identify abnormalities in cardiac function at rest, there are difficulties in obtaining an objective, unifying measurement that may be useful across all forms of heart failure. Lastly, none of these observations can identify that exercise capacity is indeed limited by cardiovascular, rather than respiratory, musculoskeletal, or motivational causes.

It may be a weakness of our conventional approach to CHF that abnormalities of exercise performance are gauged only subjectively while objective data are obtained only in the resting state. In this article, we argue that the unifying characteristic in this disease is chronic limitation of exercise aerobic response and that focusing on this may help diagnosis as well as prognostic assessment.