Infundibular pulmonic stenosis is mostly caused by overgrowth of the heart muscle wall (hypertrophy of the septoparietal trabeculae). Pulmonic stenosis is often seen as a part of Fallot' s tetralogy, in which case the events leading to the formation of the overriding aorta are also believed to be a cause of the pulmonic stenosis. The pulmonic stenosis is the major cause of the malformations seen in patients with Fallot tetralogy, with the other associated malformations acting as compensatory mechanisms to the pulmonic stenosis. The degree of stenosis varies between individuals with TOF, and is the primary determinant of symptoms and severity. This malformation is infrequently described as sub-pulmonary stenosis or subpulmonary obstruction.