The general opinion that treadmill exercise elicits circulatory reserve more than bicycle exercise derives from studies conducted in normal subjects or subjects with coronary artery disease. To investigate if this also occurs in patients with chronic heart failure (CHF), 40 patients (mean ejection fraction: 26±9 percent) with normal pulmonary function underwent in random order both treadmill (Naughton modified protocol, holding on handrails permitted) and bicycle (10 W/min) maximal exercise over a 1-week period. Peak oxygen uptake (19.6±5.3 vs 17.6±5.1 ml/min/kg, p<0.0001), ventilatory threshold (14.4±4.7 vs 12.0±3.5 ml/min/kg, p<0.0001), and minute ventilation (59±18 vs 55±15 L/min, p<0.05) were greater on treadmill than on bicycle. Heart rate, systolic blood pressure, breathing rate, respiratory exchange ratio, perceived exertion scale, and lactate were identical. The coefficient of the correlation between oxygen uptake and time was greater with bicycle than with treadmill (r=0.97±0.04 vs 0.90±0.07, p<0.001). Thus, treadmill exercise is more suitable for determining peak oxygen uptake in patients with CHF. However, the increase in oxygen uptake is more regular with bicycle exercise.