The effect of exercise training on delta Vo2/delta WR was studied in 12 patients(11 men, one woman, mean age 62 +/- 9 yr)with chronic heart failure(old myocardial infarction, dilated cardiomyopathy, patients after coronary arterial bypass graft surgery and patients after aortic valve replacement). Cardiopulmonary exercise testing was performed to decide the exercise tolerance and assess the delta Vo2/delta WR. Patients underwent physical training at the anaerobic threshold for 3 months. Cardiopulmonary exercise testing was performed after the second week and after the third month. The anaerobic threshold increased at the third month compared with before exercise testing and the second week(p < 0.05, respectively) (before exercise testing: 13.6 +/- 2.0 ml/min/kg, the second week: 14.7 +/- 2.5 ml/min/kg, the third month: 16.2 +/- 2.1 ml/min/kg). The delta Vo2/delta WR increased at the second week compared with before exercise testing(before exercise testing: 8.9 +/- 1.9 ml/min/W, the second week: 10.6 +/- 1.9 ml/min/W, p < 0.05), but significantly decreased at the third month compared with the second week(the third month: 9.4 +/- 1.7 ml/min/W, p < 0.05). Serial increase of the anaerobic threshold and the peak Vo2/heart rate suggests that the exercise tolerance and cardiac function of the patients improved significantly. The increase of the delta Vo2/delta WR after the first 2 weeks seemed to depend on the luxury blood supply to both working and non-working muscles. The decrease of delta Vo2/delta WR at the third month may be due to the redistribution of the blood flow to the working muscles.