The cardiovascular system orchestrates blood circulation to deliver oxygen and nutrients while maintaining metabolic homeostasis. This chapter concisely outlines its physiological structure and functional mechanisms, focusing on hemodynamic principles and cardiac pump regulation based on Ohm’s and Poiseuille’s laws. These laws establish that blood flow depends on pressure gradients, vascular resistance, and blood viscosity. Vascular shear stress and compliance also critically influence blood flow and tissue perfusion. Cardiac output is determined by preload, afterload, contractility, and heart rate. Cardiac contractility hinges on Ca2+-mediated excitation-contraction coupling and sarcomere mechanics, which can be analyzed via pressure-volume loops. Cardiovascular performance is further regulated by neural (sympathetic/parasympathetic) and humoral (e.g., catecholamines, renin-angiotensin system) mechanisms. Understanding these principles is essential for perioperative hemodynamic management and optimizing outcomes in children undergoing congenital cardiac surgery.