Objective: The arterial switch operation is the standard treatment for the transposition of the great arteries. The timely variation in the residual pressure gradient across the pulmonary arteries is ill-defined. This work is aimed to study the progressive changes in the pressure gradient across the pulmonary valve and pulmonary arteries after arterial switch operation (ASO). Methods: All eligible patients for this study who underwent arterial switch operation between 2000 and 2019 were reviewed. Transthoracic echocardiography (TTE), was used to estimate the peak pressure gradient across the pulmonary artery and its branches. The primary outcome was the total peak pressure gradient (TPG) which is the sum of peak pressure gradients across the main pulmonary artery and pulmonary artery branches. Furthermore, a longitudinal data analyses with mixed effect modeling were used to determine the independent predictors for the changes in pressure gradient. Results: 309 patients were included in the study. Over 17-year follow up, the freedom from pulmonary stenosis reintervention was 95% (16 out of the 309 patients underwent reintervention = 5%). the Longitudinal data analyses of serial 1844 echocardiographic studies for the included patients revealed that the TPG recorded in the first postoperative echocardiogram across pulmonary valve, right and left pulmonary artery branches was the most significant predictor for reintervention. Conclusion: The total peak gradient measured in the first postoperative echocardiogram is the most important predictor for reintervention. We propose that a total peak gradient in the first postoperative echocardiography of 55 mmHg or more is a predictor for reintervention