ObjectivesTo examine whether preoperative heart failure and cardiac surgery influence nitric oxide production and atrial natriuretic peptide (ANP) biological activity in infants and whether nitric oxide and ANP participate in the control of postoperative pulmonary vascular tone.DesignProspective, clinical study.SettingTertiary pediatric cardiac intensive care unit in a referral cardiosurgical center.PatientsNineteen infants (median age 4 months) undergoing cardiac surgery: 13 infants with ventricular or atrioventricular septal defect associated with heart failure and pulmonary hypertension (group 1); and six infants with tetralogy of Fallot, without heart failure (group 2).InterventionsBlood samples obtained from indwelling catheters or bypass circuit outlets.Measurements and Main ResultsNitrite and nitrate blood concentrations (as a marker for nitric oxide synthesis) and the molar ratio of cyclic guanosine 3 prime,5 prime-monophosphate (cGMP) to ANP (as a marker for ANP biological activity) were determined before, during, and up to 24 hrs after cardiopulmonary bypass (CPB). In group 1 patients, these biological parameters were related to postoperative pulmonary arterial pressure.Preoperative nitrite and nitrate concentrations were higher in group 1 patients than in group 2 patients (p < .02), and this difference persisted during CPB. Nitrite and nitrate concentrations 24 hrs postoperatively were lower than preoperative values in group 1 patients (p < .05) and were unchanged in group 2 patients. An inverse correlation was observed postoperatively between nitrite and nitrate concentrations and systolic pulmonary arterial pressure (r2= 0.4, p < .05). Group 1 patients had a lower preoperative cGMP/ANP ratio than group 2 patients (p < .05), despite higher ANP levels (p < .005). The cGMP/ANP ratio decreased during CPB in both groups (p < .0001), and in group 2 patients, cGMP and ANP values remained below preoperative values <or=to24 hrs postoperatively. A correlation was observed between ANP levels and systolic pulmonary arterial pressure 2 and 4 hrs postoperatively (r2= .4, p < .05, respectively), but no correlation was observed between ANP biological activity and postoperative pulmonary arterial pressure.ConclusionsInfants with heart failure and pulmonary hypertension have increased nitric oxide synthesis and decreased ANP biological activity; both phenomena may be involved in the pathophysiology of this clinical condition. CPB has no detectable effect on nitric oxide production but does decrease ANP biological activity. In patients with preoperative heart failure and pulmonary hypertension, endogenous nitric oxide appears to play a role in the control of postoperative pulmonary vascular tone. (Crit Care Med 1997; 25:1063-1070)