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Reduction of pulmonary vascular resistance and maintenance of urine output are important after the modified Fontan procedure. Atrial natriuretic peptide (ANP) has the effects of a vasodilator (including the pulmonary arteries) and a physiologic diuretic, and newly synthesized human ANP is available. We measured plasma ANP levels before and after the Fontan procedure and examined the effects of human ANP on hemodynamic parameters after the Fontan procedure.Eight patients, aged 2 to 15 years, underwent the Fontan procedure (atriopulmonary connection). Blood samples were taken before and 3 hours after operation, and plasma ANP levels were measured by radioimmunoassay. The correlation between central venous pressure and ANP was examined. Human ANP was infused intravenously at a dosage of 0.1 μg · kg−1 · min−1 for 1 hour after the Fontan procedure under controlled ventilation and another blood sample was obtained. Urine volume and central venous pressure were measured, and pulmonary vascular resistance and the cardiac index were calculated by the thermodilution catheter method before and after human ANP infusion. One hour after human ANP infusion was discontinued, the evaluation was repeated. No other diuretics were given and the infusion rates of catecholamine were kept constant during these measurements.Plasma ANP levels before and after the Fontan procedure were 29.1 and 54.9 pg/mL, respectively, and a positive correlation was obtained between central venous pressure and plasma ANP levels (r = 0.661, p < 0.05). Human ANP infusion significantly decreased central venous pressure and pulmonary vascular resistance, and increased urine volume and the cardiac index, whereas the plasma ANP level was elevated to 617.5 pg/mL. Systemic blood pressure did not change significantly.Atrial natriuretic peptide is secreted in response to elevated central venous pressure after the Fontan procedure, but its concentration might not be sufficient. Human ANP can be a therapeutic choice after the Fontan procedure as a physiologic diuretic and a pulmonary vasodilator.