This study assessed the relationship between the VO2 measured at ventilatory threshold (VT) and the VO2 measured at the point of deflection from linearity of heart rate (HRD). Twelve children (10 boys and 2 girls) with a mean age of 11.3 years (± 4.8) performed a graded exercise test to determine VT and HRD. All children had undergone surgical repair for d-transposition of the great arteries at approximately 13 months of age. Because of failure to demonstrate HRD, the data from 4 patients were excluded from statistical analysis. For the remaining 8 patients there was no significant difference between mean VO2 (ml/kg/min) at VT and HRD (26.6 ± 6.4 vs. 26.3 ± 6.8; p > 0.25). Linear regression analysis revealed a correlation of r = 0.92 between the VO2 measured at VT and the VO2 measured at HRD. Only 8 of the 12 patients (66%) in this study satisfied criteria needed to identify the HRD. Therefore HRD may be an accurate predictor of VT in most but not all children who have had surgery for d-transposition of the great arteries.