In 1947 Thomas Holmes Sellors (1902–1987) of the Middlesex Hospital operated on a Fallot's Tetralogy patient with pulmonary stenosis and successfully divided the stenosed pulmonary valve. In 1948, Russell Brock, probably unaware of Sellor's work, used a specially designed dilator in three cases of pulmonary stenosis. Later in 1948 he designed a punch to resect the infundibular muscle stenosis which is often associated with Fallot's Tetralogy. Many thousands of these "blind" operations were performed until the introduction of heart bypass made direct surgery on valves possible.