Background Right ventricular function may be an important determinant of exercise capacity, peak oxygen consumption (Vo2), and the ventilatory response to carbon dioxide production (Ve/Vco2relation) in patients with chronic heart failure (CHF).Methods and Results We studied the role of right ventricular function in CHF and also investigated the effects of absent right ventricular reserve in patients previously operated on with Fontan's procedure by measuring metabolic gas exchange during exercise in five groups of patients:(1) 10 patients who had previously undergone Fontan's procedure for congenital heart disease in whom the right ventricle is not functional; (2) 11 age-matched control subjects with dilated cardiomyopathy (DCM); (3) 15 age-matched normal subjects; (4) 42 patients with CHF; and (5) 16 age-matched control subjects. Left and right ventricular ejection fractions (LVEF and RVEF) were measured by radionuclide ventriculography in group 4. In the young subjects, the Ve/Vco2slope was lower in the control subjects than in the other two groups, being 24.4+-4.3 against 33.3+-6.6 in group 1 (P<.001) and 29.6+-8.1 in group 2 (P<.05). The correlation between peak Vo2and Ve/Vco2was -0.80 (P=.005) in group 1 and -0.76 (P=.007) in group 2. In the older age groups, the Ve/Vco2slope was significantly greater (38.0+-14.9 versus 25.4+-3.7; P<.001) in the heart failure group (group 4). In neither control group was there a significant relation between peak Vo2and Ve/Vco2slope. In group 4, the relation between peak Vo2and Ve/Vco2was similar to that seen for groups 1 and 2. LVEF was 24.3+-14.1%, and RVEF was 32.5+-13.1%. There was no correlation between either RVEF or LVEF and peak Vo2or Ve/Vco2slope in the heart failure group.Conclusions The relation between excessive ventilation and reduction in peak oxygen consumption is present in patients with no functioning right ventricle.RVEF is not a determining feature of either exercise capacity or the excessive ventilatory response in CHF. (Circulation. 1994;89:2062-2069.)