Children with right-to-left shunts have cyanotic lesions. Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart defect. The cardiac anomalies that present with TOF are a narrow right ventricular outflow tract, a ventricular septal defect, and an overriding aorta. Deoxygenated blood flow exits the right ventricle where it meets obstruction as it tries to flow into the pulmonary artery. Following the path of least resistance, some of the blood then flows across the ventricular septal defect (a right-to-left shunt), where it passes into the aorta, having never gone to the lungs to obtain oxygen. Depending on the degree of right ventricular outflow tract obstruction, the child will have varying degrees of cyanosis and decreased oxygen saturation readings.