Pulmonary Stenosis (PS) - Pulmonary stenosis causes obstruction of blood flow from the right ventricle to the pulmonary arteries. This obstruction causes the right ventricle to have more difficulty pumping oxygen-poor blood received from the vena cava to the lungs in order to capture the necessary oxygen. Thus causing a decrease in oxygen exchange in the lungs, as well as a decrease in blood volume to the lungs.3. Dominant Aorta – Due to the alignment of the ventricular septum and the formation of the VSD, the aorta is placed “directly above the aorta”. Both the right and left ventricles have access to the aorta, resulting in increased blood flow to the aorta. Due to pulmonary stenosis of the pulmonary arteries, blood flow to the lungs will be obstructed, causing blood to flow back to the right ventricle and back to the aorta; mix the oxygenated blood with the deoxygenated blood going to the body tissues.4. Right ventricular hypertrophy (RVR) – In a normal heart, the left ventricle has a slightly thicker wall than the right because it needs to pump oxygenated blood to the body, unlike the right ventricle which only needs to pump blood deoxygenated. to the lungs. However, tetralogy of Fallot causes hypertrophy of the right ventricular muscle due to pulmonary stenosis of the lung.