In Tetralogy of Fallot, the pathway through which the blood leaves the right lower chamber (ventricle) is small, as is the pulmonary valve, making it hard for blood to pass through to the lungs. In addition, there is a large hole in the wall between the heart’s right and left ventricles (ventricle septal defect, or VSD). And, the aortic arch, the vessel that connects the ascending and descending sections of the aorta may be abnormally oriented toward the right, rather than the left, as it normally is. This is called “right aortic arch.”