In-depth knowledge of cardiovascular physiology is essential for delivering optimal care to patients undergoing cardiac surgery. The cardiovascular system’s core function is to supply the body with oxygen and nutrients while removing carbon dioxide and waste products. Its key components include the heart, blood, blood vessels, and lymphatic system. This chapter provides a comprehensive overview of crucial aspects of cardiovascular physiology. It delves into the unique properties of cardiac muscle, the electrical activity that drives the heartbeat, the intricate process of excitation–contraction coupling that converts electrical signals into mechanical pumping, the cyclical nature of the cardiac cycle, the dynamics of cardiac output, and the complex mechanisms that regulate blood pressure. Understanding these fundamental principles is crucial for comprehending the physiological changes that occur during cardiac surgery and for making informed decisions regarding patient management and treatment strategies.