When caring for patients with congenital heart disease (CHD), it is crucial to understand concepts of fetal and neonatal cardiovascular physiology, as well as the anatomy and pathophysiology of common cardiac lesions and their evolution over time. This knowledge is essential for perioperative care and risk stratification of this patient population from birth to adulthood. While some congenital heart defects involve purely obstructive or regurgitant valvular lesions, the presence of shunts (both physiologic and anatomic) is a hallmark of CHD. It is important to clearly understand the concepts of shunting (both physiologic and anatomic), single-ventricle physiology, and intercirculatory mixing. In addition, this chapter will address the anatomy, physiology, and treatment of commonly encountered congenital heart lesions.