The pharmacodynamic and pharmacokinetic profiles of high-dose sufentanil (15 micrograms/kg) and oxygen were determined in 20 infants and children undergoing repair of congenital heart defects. Sufentanil provided marked hemodynamic stability after an infusion and during the stress periods of incision and sternotomy. Two patients required supplemental nitrous oxide because of an increase in blood pressure greater than 20% of baseline. Mean plasma catecholamine concentrations varied widely among patients and increased, although not significantly, during intraoperative stress. Pharmacokinetic data best fit a two-compartment model. In infants younger than 10 months (group 1) and children older than 10 months (group 2) who were not surface-cooled, elimination half-lives were similar (mean +/- SD, 53 +/- 15 min vs 55 +/- 10 min) as were clearance values (27.5 +/- 9.3 vs 18.1 +/- 10.7 ml X kg-1 X min-1). However, the volumes of distribution were significantly smaller in group 1 compared with group 2 (1.6 +/- 0.46 vs 3.0 +/- 1.3 L/kg). In infants younger than 10 months who were surface-cooled (group 3) elimination half-life was longer (120 +/- 36 min) and volume of distribution larger (3.7 +/- 1.1 L/kg), but clearance rate was similar (21.5 +/- 5.0 ml X kg-1 X min-1) compared with age- and weight-matched infants (group 1).