Understanding the pathophysiological changes in congenital heart disease (CHD) is crucial for perioperative anesthesia management in pediatric CHD patients. This chapter concisely outlines the key pathophysiological mechanisms, including shunting, obstructive, mixed, and regurgitant lesions, alongside myocardial ischemia and pulmonary hypertension (PH). Left-to-right shunts increase pulmonary blood flow and volume load, while right-to-right shunts cause hypoxemia. Obstructive lesions may lead to pressure overload and myocardial ischemia. Mixing lesions rely on intercirculatory blood mixing regulated by systemic-to-pulmonary vascular resistance ratios. Regurgitant lesions can lead to cardiac volume overload and progressive functional decline. Coronary anomalies or supply-demand imbalance may result in myocardial ischemia, while increased pulmonary vascular resistance or elevated pulmonary blood flow can cause PH. Therefore, perioperative anesthetic management requires balancing systemic and pulmonary vascular resistances, maintaining cardiac output, optimizing oxygenation, and tailoring individualized strategies to optimize outcomes.