Tetralogy of Fallot consists of four abnormalities. First, there is a narrowing at the right ventricular outflow, ranging from the entrance of the right ventricular infundibulum to the branches of the left and right pulmonary arteries. Second, there is a ventricular septal defect, characterized by a deficiency around the membranous part that extends towards the outflow. Third, the aorta overrides, where the base of the aorta is enlarged and rotates clockwise to the right, straddling the septal defect. Fourth, right ventricular hypertrophy, which is a secondary lesion.