Background: Pulmonary arterial hypertension (PAH) is a frequent complication of congenital heart disease (CHD) with left-to-right shunt. Increased pulmonary pressure leads to vascular remodeling and RV dysfunction. Objectives: To analyze the role of  high-sensitive cardiac  troponin T (hs -cTnT) in the determination of myocardial injury caused by volume and pressure load due to pulmonary hypertension (PH) in children with left to right cardiac shunt. Patients and Methods: Twenty  patients with congenital heart disease (CHD) with left to right shunt and PAH-CHD, 20 patients with CHD with left to right shunt but without PH, and 20 healthy children, in total 60 individuals, were included in the study. All cases aged between 3 and 36 months. Plain x-ray chest and heart, electrocardiography, Doppler and Two –dimensional, M- mode echocardiographic evaluation of CHD and pulmonary pressure were performed in all patients. Blood samples were obtained from all cases for measurement of serum high-sensitive cardiac troponin T (hs-cTnT) levels by highly sensitive third-generation quantitative test. Results: The mean hs-cTnT levels were significantly higher in patients with PH than in patients without PH (p < 0.05) with a sensitivity 70% and specificity 95%. A statistically significant positive correlation was determined between pulmonary artery pressure and hs-cTnT levels, and significant negative correlation with EF% and FS %( by echocardiography). Conclusions: Serum levels of high-sensitive cardiac troponin T (hs-cTnT) were significantly elevated in PAH-CHD children denoting myocardial injury caused by volume and pressure load due to PH in children with left to right cardiac shunts, so it could be used as a cardiac biomarker in PAH-CHD children with good diagnostic and prognostic value and high sensitivity and specificity, which may be useful in the management of PH in childhood.