Aims: Physical training is considered to be safe and beneficial as part of the treatment in heart failure patients. Prospective, sufficiently large studies are still needed to confirm this hypothesis., Methods: In a prospective study, 80 patients with chronic heart failure class II and III (age, 56.6+/-8.3 years; left ventricular ejection fraction, 26.5+/-9.6%) were randomized to an endurance training group or to a control group with continuation of optimal pharmacological treatment., Results: No training-related adverse event was reported, implying that the training programme was safe for these groups of chronic heart failure patients. Between-group comparison of changes revealed that training increased exercise time (from 608+/-35 to 738+/-40 s, P<0.0001), anaerobic threshold (from 10.5+/-0.4 to 11.8+/-0.3 ml x kg-1 min-1, P<0.05), and decreased the ventilatory equivalent for carbon dioxide at submaximal exercise level (from 2.8+/-0.1 to 2.7+/-0.1, P<0.05). Training did not increase peak oxygen consumption (15.2+/-0.5 to 16. 6+/-0.5 ml x kg-1 min-1, ns). An improvement in patients' assessment of quality of life was observed. There was a significant correlation between physiological and psychological improvements. Training was not effective in patients whose exercise test at entry had a duration of less than 7 min. None of the other baseline data could predict an effective training response., Conclusion: Physical training in chronic heart failure patients class II and III is safe and results in significant improvements in exercise time, anaerobic threshold, ventilatory equivalent for carbon dioxide at submaximal exercise level and quality of life., (Copyright 1999 The European Society of Cardiology.)