Lung function and pulmonary regurgitation limit exercise capacity in postoperative tetralogy of Fallot. Fifty-five patients with repair of tetralogy of Fallot were evaluated with treadmill exercise, pulmonary function testing and rest two-dimensional and Doppler echocardiography to determine the relation among cardiopulmonary function, exercise capacity and ventricular arrhythmias. The mean age at repair was 8.1 +/- 2.1 years; age at the time of study ranged from 15 to 37 years (mean follow-up time after repair 18 +/- 5 years). Exercise duration was 92 +/- 17% of predicted. Maximal heart rate was 94 +/- 7% of predicted. No exercise test was stopped because of an arrhythmia. Thirty patients had oxygen consumption and ventilation measured during their final minute of exercise. Peak oxygen consumption was 31 +/- 8 ml/kg per min (86 +/- 18% of predicted). Twenty-five patients (45%) had low vital capacity at rest (less than 80% of predicted). Pulmonary regurgitation was identified in 42 (75%) of the patients and judged to be moderate in 10 (18%). Mild tricuspid valve regurgitation was identified in 64%. Doppler estimated right ventricular outflow gradient was greater than 15 mm Hg in 15% of the patients (mean gradient 24 mm Hg [range 16 to 56]). Age at repair, duration of follow-up and type of repair did not correlate with echocardiographic variables, ventilatory data, exercise performance or arrhythmias. Moderate pulmonary regurgitation was associated with increased right ventricular diastolic area and both were inversely related to exercise duration and vital capacity. Decreased breathing reserve during maximal exercise was associated with moderate pulmonary regurgitation and decreased vital capacity. The results indicate that exercise capacity in these patients is in general good; however, right ventricular volume loading and ventilatory dysfunction may produce exercise limitation. 