Five patients with ages ranging from 6 months to 3 years were analyzed. All received inhaled nitric oxide (NO - 20 parts per million (ppm)) and oxygen (O2 - at a concentration of 90-95 percent) by means of an oxygen hood. Mean Pulmonary Artery Pressure (MPAP), Mean Aortic Pressure (MAoP), Pulmonary Vascular Resitance (PVR) and Systemic Vascular Resistance (SVR) were measured and the calculation of their relationship to pulmonary/systemic flow (Qp/Qs) was performed by the catheterization of the femoral artery vein. Three patients presented reduction in PVR and increase in Qp/Qs. There were no systemic alterations or any side effect from using NO.