Background: Congenital heart diseases are abnormalities of the heart and/or great vessels present at birth. 1% of live births have a congenital heart defect. Cardiac Troponin, especially cardiac Troponin I (cTnI), are the preferred biomarkers for the detection of cardiac injury. International cardiology and laboratory medicine guidelines recommend highly sensitive Tn1 (hscTnI) that has excellent precision (<10%). hsTnI is a cheap way that is capable of accurately and precisely detecting low levels of Troponin I enabling treatment and allowing earlier definitive diagnosis of acute myocardial injury than is currently possible. Objectives: Evaluation of the myocardial injury as detected by highly sensitive cardiac Troponin I (hscTnI) in children with left to right shunt. Patients and methods: This cross-sectional study was conducted on 48 patients with congenital heart diseases (CHD) whether cyanotic or acyanotic diagnosed clinically and by echocardiography admitted to Cardiology Unit of Pediatric Department, Zagazig University Hospitals from June 2017 to December 2017. Their ages ranged from 2 months to 4 years. hscTnI assay was performed for all patients. Results: The study revealed that patients' group with CHD with left to right shunt had high level of hscTnI with a median range from 1.7-237.00 ng ml. Conclusion: Serum Troponin I levels were high in children with CHD with left to right shunt, which may indicated underlying myocardial injury.