This document discusses the anatomy and function of the heart. It begins by reviewing heart formation during embryogenesis from mesoderm layers. It describes the circulation pathway of oxygenated and deoxygenated blood through the heart chambers and valves. Common congenital heart defects are explained, including ventricular septal defects which cause a hole between the ventricles. Signs of VSDs include heart murmurs and difficulties maintaining weight from the extra blood flow to the lungs. Untreated large VSDs can lead to heart failure or pulmonary hypertension.