Many of the symptoms of heart failure (breathlessness and fatigue) are not primarily due to reduced cardiac output, but relate to an impairment of peripheral muscle performance and metabolic efficiency. With regular training it is possible to increase skeletal muscle performance through improvements in muscle efficiency. Recent data suggest that such improvements may be modulated by local tissue renin-angiotensin systems and, in particular, by the local activity of angiotensin-converting enzyme (ACE). These findings might explain the remarkable benefits of ACE inhibition in the treatment of heart failure.