Background: Pulmonary hypertension is defined as a resting mean pulmonary artery pressure (mPAP) of 25 mmHg or above. PAH is a frequent complication of congenital heart disease (CHD), particularly in patients with left-to-right (systemic-to-pulmonary) shunts. Objective: The present study aimed to investigate changes in the blood level of endothelin-1 (ET-1) in patients of PAH complicated by acyanotic CHD and to detect possible correlation with different hemodynamic parameters. Patient and methods: 48 children were recruited in Pediatric Cardiology Unit, Pediatrics Department in Zagazig University Hospitals after obtaining the required permissions and informed consent from the their caregivers. They were divided into Group (A), which included 24 children with acyanotic CHD with left to right shunt with PAH and Group B included 24 children with acyanotic CHD with left to right shunt but no PAH. All children were subjected to clinical and radiological examination, echocardiography and measurement of endothelin-1 level as well as correlation between the studied parameters were performed. Results: the present results showed that Group A was significantly associated with previous need of hospital admission and insignificantly associated with ICU need. Endothelin-1 was significantly negatively correlated with weight and oxygen saturation (SPO₂) but significantly positively correlated with systolic blood pressure (SBP), heart rate (HR), respiratory rate (RR) and pulmonary blood pressure. Significant area under the curve (AUC) with cutoff value >1.55 with sensitivity 85.05 and specificity 91.1%. Conclusion: Pulmonary hypertension (PAH) complicated by CHD can be predicted by estimation of endothelin-1 (ET-1) as an indicator of endothelial injury.