Discordance exists between apparently reduced systemic right ventricular function and the reported asymptomatic state of many patients after atrial repair for transposition of the great arteries. To evaluate this clinical observation, cardiopulmonary response to exercise in 17 asymptomatic patients with no significant postoperative hemodynamic abnormalities was assessed by upright bicycle ergometry according to a modified Jomes protocol 11.5 +/- 1.5 years after Mustard atrial repair. Seventeen age- and sex-matched normal adolescents constituted the control group. Incremental exercise was performed to determine maximum work capacity, heart rate, blood pressure, oxygen saturation, and minute ventilation. Cardiac output was computed at rest and during steady-state exercise by a carbon dioxide rebreathing method at 50% of the maximum workload achieved during incremental exercise. Height and weight were similar in patients and controls (p greater than .05). Resting pulmonary function variables were normal in all subjects. At peak exercise, respiratory quotient was greater than 1 in both patients and controls (1.12 +/- 0.09 and 1.09 +/- 0.08 respectively, p greater than .05). Patients achieved a lower peak heart rate (172 +/- 14 vs 185 +/- 11 beats/min, p less than .01), lower maximum work capacity (2.3 +/- 0.6 vs 3.3 +/- 0.7 W/kg, p less than .01). The ratio of minute ventilation at peak exercise to maximum resting voluntary ventilation was normal (less than or equal to 80%) in both groups. The ventilatory equivalent for oxygen was similar at rest, but significantly higher in patients than in control subjects at peak exercise (42 +/- 7 vs 36 +/- 5, p less than .006).(ABSTRACT TRUNCATED AT 250 WORDS)