This document provides information about congenital heart diseases. It discusses cyanotic heart diseases like tetralogy of Fallot and hypoplastic left heart syndrome, which allow deoxygenated blood to bypass the lungs. It also covers acyanotic heart diseases, where blood is pumped abnormally but still receives enough oxygen. Common cyanotic defects involve obstructions or mixing of blood flows. Hypoplastic left heart syndrome is a rare defect where the left side of the heart is underdeveloped. Tetralogy of Fallot is the most common cyanotic defect, consisting of four abnormalities. Early surgery is often needed to correct these defects.