Introduction: Endothelial dysfunction in Chronic Heart Failure (CHF) secondary to congenital systemictopulmonary shunts (CSPS) associated with Pulmonary Arterial Hypertension (PAH) leads to chronically impaired production of vasodilator and antiproliferative agents such as NO, along with overexpression of vasoconstrictor and proliferative substances - endothelin1 (ET-1). The purpose of the study: Emphasizing the pathophysiological particularities of NO and ET-1 in CHF secondary CSPS associated with PAH. Methods and materials: In the study were included 70 children with CHF secondary to CSPS associated with PAH (mean age 37,4±3,4 months). Taking into the consideration the level of PAH, these children were divided into 2 groups: first group – 16 children with CHF and PAH moderate, and second group – 54 children with CHF and PAH severe. The third group - 16 children with CHF and without PAH. In the witness group were included 15 health children, with innocent cardiac murmur. The groups were comparable taking into account the age and sex. NO and ET-1 were determined by the ELISA method (DRG International Inc., SUA). Results: At patients with CHF and PAH moderate the level of NO was higher - 116,45±6,1 mol/l with respect to the values of NO at children with PAH severe 93,06±3,34 (p<0,05) and to those with CHF but without PAH - 90,91±4,07 (p<0,05), and versus the healthy children - 77,32±5,1 (p<0,001). In PAH severe the pulmonary vasodilatator mechanisms with the diminishing of NO get worse. ET-1 has had higher values in children with PAH severe - 7,78±0,28 pg/ml with high statistical significance with respect to patients with PAH moderate - 3,88±0,21, versus those without PAH - 3,69±0,24 (p<0,001) and those healthy - 2,9±0,27 (p<0,001). The hemodinamic stress within the CSPS asociated with PAH are responsabile of the endothelium’s lesion which conducts to the stimulation of ET-1 production by the endothelium cells. Conclusions: The obtained results suggest the important role ET-1 and NO in pathophysiology of PAH secondary to CSPS with CHF. At patients with CHF and PAH severe the endothelium’s lesion causes a disbalance between the production of the mediators with vasodilators effects and those with vasoconstrictor properties; the NO level being significantly higher at patients with PAH moderate versus those with PAH severe, while the ET-1 values were higher at children with PAH severe with respect to those with a moderate level and without PAH.