To define the relation between atrial natriuretic peptide (ANP) and hemodynamic parameters in children with pulmonary artery hypertension, we measured the ANP concentrations of the femoral vein, right atrium, pulmonary artery, left atrium and left ventricle, or femoral artery in 32 patients during right or left heart catheterization. There is a strong correlation among the ANP levels obtained from different locations (p < 0.001), and these ANP levels are positively correlated with pulmonary arterial pressures and pulmonary resistance. Patients were divided into two groups according to their pulmonary arterial pressure. The group with pulmonary arterial systolic pressure higher than 31 mmHg had higher ANP levels than the group with pulmonary arterial systolic pressure lower than 31 mmHg. When patients were grouped according to their pulmonary resistance, ANP levels in the group with pulmonary-resistance over 2 U/m2 were higher than those in the group with pulmonary resistance lower than 2 U/m2. In this study ANP levels showed a correlation with the right ventricular systolic pressure. A correlation was not seen between ANP levels and the flow ratios or the presence of shunt. The results of our study suggest that ANP should be considered an important factor in pulmonary hypertension, independent of other factors.