Ergospirometry was performed in 19 children and adolescents operated for tetralogy of Fallot (TOF) to assess their exercise capacity compared to an active non sportive control group. The test was carried out on a treadmill with measurement of oxygen consumption cycle by cycle throughout exercise. In comparison with the control group, the patients had: a working capacity which was normal or reduced by 30 to 40 p. 100; a decrease d'oxygen consumption (-30 to 40 p. 100) throughout exercise and at maximal effort: this corresponds to a lower stroke volume secondary to the absence of physical activity during childhood and/or residual cardiac lesions; abnormal chronotropism: the test was stopped at a lower heart rate corresponding to a fall in oxygen uptake during exercise, or to an increase in the systolic ejection period probably due to right ventricular dysfunction or to the patient reaching maximal ventilation; decreased maximal ventilation capacity due to a lower tidal volume and a higher respiratory rate. This type of ventilation increases to role of the dead space and may be related to progressive "pulmonary dysfunction" or secondary to residual cardiac lesions. These different parameters cannot be assessed by simple ergospirometry: the test must be coupled with an evaluation of ventilatory function on effort in order to control and evaluate the long term functional results and the aptitude of these patients to regular physical activity.