The procedure was made possible by the newly-developed heart-lung machine, before the advent of which there was no means of cutting into the heart without killing the patient. Operations had thus been limited to procedures on the intact beating heart, for example widening the mitral valve with a dilator.
In the early 1950s Professor Ian Aird, under whom Bentall worked at the Royal Postgraduate Medical School at Hammersmith Hospital, had the idea of creating an artificial heart and lung that would operate as a bypass outside the body and take over the vital job of pumping and oxygenating the blood. With his support Denis Melrose, a lecturer (later Professor) at the school, set about designing a machine that would enable the surgeon to operate on a bloodless (though still beating) organ and repair defects such as holes in the heart. In collaboration with the medical instrument firm New Electronic Products (NEP), Melrose developed a machine which became known as the Melrose-NEP heart-lung machine.
Bentall and Cleland carried out the first operation using the machine on a human in Britain. It was a complete success; 25 years later the patient was still in good health. Within four years Bentall and his colleagues were routinely carrying out open-heart surgery on a variety of patients, and the apparatus was being introduced into other hospitals across the country and around the world.
Bentall’s first post was in general surgery under Ivor Lewis at the North Middlesex Hospital, where he assisted with the first successful pulmonary embolectomy (the surgical removal of clotted blood blocking blood circulation to the lungs) and the first anatomical correction of oesophageal atresia (a congenital defect affecting the alimentary tract) in Britain. He then became Chief Resident at the London Chest Hospital, doing thoracic surgery, until he joined the Royal Navy in 1945. He served in a naval hospital and then in Empire Clyde — the only hospital ship in the British Pacific Fleet during the war.
After demobilisation in 1947 he taught anatomy at the Charing Cross Hospital Medical School until 1950, when he joined the Royal Postgraduate Medical School at Hammersmith Hospital as chief assistant to Aird, doing general and thoracic surgery and research to develop cardiac surgery.
The development of open-heart surgery excited interest around the world, and in April 1959, with Denis Melrose, Bill Cleland and other members of the Hammersmith cardiac team, he accepted an invitation to travel to Moscow to demonstrate the new technique to Russian surgeons at the Institute of Cardiovascular Surgery in Leninsky Prospekt.
After travelling on the Soviet Ship Baltika with half a ton of equipment, the team carried out five open-heart operations, on adults and children, watched by more than 200 surgeons from across the Soviet Union. This was probably the first time that a group of foreign doctors had actually worked in the Soviet Union, and the visit was well covered in the British press, making the front page of The Daily Telegraph.
In 1962 Bentall and his team appeared in the first episode of the classic BBC documentary series, Your Life in Their Hands, in which he performed an operation to repair a hole in the heart. Three years later Bentall was appointed the first Professor of Cardiac Surgery in Britain, at the Royal Postgraduate Medical School.