OBJECTIVE: The increase in intrathoracic pressure produced by positive-pressure ventilation has been shown to have an adverse effect on pulmonary blood flow after Fontan operations. OBJECTIVE: The main objective was to compare the hemodynamic effect of high-frequency oscillation ventilation (HFOV) with intermittent positive-pressure ventilation (IPPV) in children after Fontan operations. DESIGN: Prospective study. SETTING: Department of pediatric critical care in a tertiary care, university-based children's hospital. PATIENTS: Five children (age, 2.3 +/- 0.3 yrs) in the early period after Fontan operations. INTERVENTION: After a short period of stabilization after surgery using conventional IPPV, baseline data were collected and patients were converted to HFOV. After a short period of stabilization using HFOV, a second series of measurements were performed and patients were reconnected to IPPV, after which a third series of measurements were made. Paco(2) and pH were kept unchanged throughout the study. MEASUREMENTS AND MAIN RESULTS: Hemodynamic and respiratory variables were obtained at each time point (IPPV1, HFOV, and IPPV2). The mean cardiac index at baseline (IPPV1) was 3.1 +/- 1.1 L/min/m(2); during HFOV, it was 3.2 +/- 1.2 L/min/m(2) (p =.46); and during IPPV2, it was 3.1 +/- 1.1 L/min/m(2). The mean pulmonary vascular resistance values using IPPV1, HFOV, and IPPV2 were 3.0 +/- 1.1, 2.7 +/- 1.3 (p =.21), and 2.6 +/- 1.1 Woods units/m(2), respectively. CONCLUSION: HFOV had no effect on the cardiac output or the pulmonary vascular resistance in a small group of stable patients after Fontan operations.