Aims Benefit from exercise training in heart failure has mainly been shown in men with ischaemic disease. We aimed to examine the effects of exercise training in heart failure patients less than or equal to 75 years old of both sexes and with various aetiology. Methods and Results Fifty-four patients with stable mild-to-moderate heart failure were randomized to exercise or control, and 49 completed the study (49% greater than or equal to 65 years; 29% women; 24% non-ischaemic aetiology; training, n=22; controls, n=27). The exercise programme consisted of bicycle training at 80% of maximal intensity over a period of 4 months. Improvements vs controls were found regarding maximal exercise capacity (6+/-12 vs -4+/-12% [mean+/-SD], P<0.01) and global quality-of-life (2 [1] vs 0 [1] units [median {inter-quartile range}], P<0.01), but not regarding maximal oxygen consumption or the dyspnoea-fatigue index. All of these four variables significantly improved in men with ischaemic aetiology compared with controls (n=11). However, none of these variables improved in women with ischaemic aetiology (n=5), or in patients with non-ischaemic aetiology (n=6). The training response was independent of age, left ventricular systolic function, and maximal oxygen consumption. No training-related adverse effects were reported. Conclusion Supervised exercise training was safe and beneficial in heart Failure patients less than or equal to 75 years. especially in men with ischaemic aetiology. The effects of exercise training in women and patients with non-ischaemic aetiology should be further examined.