Multiple compensatory mechanisms operate to preserve exercise tolerance in patients with left ventricular failure. Exercise capacity of most patients with chronic heart failure is limited by dyspnea or fatigue, or both. Maximal stress testing with direct assessment of peak O2 uptake is an essential measurement in planning exercise conditioning programs, which are now attracting patients with chronic heart failure. The biochemical and histologic patterns of skeletal muscle changes seen in chronic heart failure patients are consistent with the effects of long-term exercise deconditioning in normal subjects. Recent studies have suggested beneficial effects of training in subjects with moderate or even severe left ventricular dysfunction by showing increased exercise tolerance or peak O2 consumption, anaerobic threshold, peak leg blood flow, peak central arteriovenous oxygen difference and decreased lactate accumulation. However, a number of questions remain unanswered. Exercise training for the treatment of chronic heart failure should be determined on an individual basis and used with caution.