Objective: The aim of this study was to determine the usefulness of the Tei Index, an echocardiographic parameter, in the early determination of pulmonary artery pressure (PAP) in congenital heart disease (CHD) with a left-to-right shunt. Methods: Right and left ventricular functions were evaluated using Tei Index values determined with tissue Doppler echocardiography. Cardiac catheterization was performed in all cases. The presence of pulmonary arterial hypertension (PAH) was defined as a mean PAP of ≥25 mm Hg and a pulmonary vascular resistance index of >3 WU/m2. Patients with a pulmonary/systemic blood flow ratio of ≥2 were considered candidates for surgery. Results: The Tei Index values measured from the left ventricular posterior wall and the right ventricular anterior wall were found to be significantly higher in the patients with PAH (0.68±0.18, 0.67±0.16, respectively) compared with the patients without PAH (0.56±0.16, p=0.027; 0.51±0.12 p=0.001). A significant correlation was detected between the Tei Index value measured from the left ventricular posterior wall and the mean PAP (correlation coefficient: 0.491). Conclusion: The right ventricular Tei Index values in children with CHD and a left-to-right shunt can be used as a parameter to follow up on the potential development of PAH, to make a diagnosis in the early period, and to make a timely decision about surgery.