Background: Development of pulmonary hypertension commonly accompanies congenital heart disease; nitric oxide (NO) is evidently an important mediator of pulmonary vascular reactivity.
Objective: Investigate the effect of pulmonary hypertension (PH) associated with congenital heart disease on NO production.
Material and Method: The authors measured plasma levels of nitric oxide-related compounds in 28 patients, aged 3 months to 12 years with congenital heart disease (CHD) and increased pulmonary blood flow. Blood samples were obtained during their cardiac catheterization. The subjects were subsequently divided into two groups, namely: group 1 CHD were those with left-to-right shunt; and group 2, CHD with right-to-left shunt.
Results: Four patients had severe pulmonary hypertension (mean pulmonary arterial pressure >60 mmHg). The total levels of NO-related compounds between the two groups were not statistically different as well as the levels in pre- and post-pulmonary artery. In patients with left-to-right shunt with mild to moderate pulmonary hypertension, the levels of total NO-related compounds were directly correlated with the level of pulmonary arterial pressure and pulmonary vascular resistance (r = 0.67; p-value < 0.05, and r = 0.75; p-value < 0.05). Additionally, in patients with severe pulmonary hypertension, the levels of total NO-related compounds decreased when compared to the levels in patients with mild to moderate pulmonary hypertension.
Conclusion: The present results suggested that the hemodynamic status of the pulmonary circulation in congenital heart defect is at least partly correlated with the blood levels of nitric oxide. 

Keywords: Plasma nitric oxide, Pulmonary arterial pressure, Congenital heart disease