Denis Melrose played a crucial role in designing and developing the first heart-lung machine. He was born in Cape Town on 20 June 1921, the son of Thomas Robert Gray Melrose, a surgeon, and Floray Collings. The family went to England before the Second World War, and Denis was educated at Sedbergh and University College, Oxford, going on to University College Hospital for his clinical studies. There he was taught by Sir Thomas Lewis, the cardiologist. After qualifying, he did junior jobs at Hammersmith and Redhill County Hospital, Edgware, before serving in the RNVR from 1946 to 1948. He returned to the Royal Postgraduate Hospital Hammersmith as a lecturer when Ian Air was the professor of surgery. Air encouraged Melrose in his dream of making a heart-lung machine. At that time a Hungarian refugee, Francis Kellerman, had set up a medical instrument firm called New Electronic Products (NEP) and generously offered to collaborate with Melrose in designing the Melrose-NEP heart-lung machine. This was first used at Hammersmith in 1957 on a patient with an atrial septal defect, who survived more than 25 years. The machine was soon used in other UK centres, New Zealand and Australia. In 1959 a group of Russian surgeons visited Hammersmith, decided to buy a Melrose machine, and Denis accompanied a team which included Bill Cleland, Hugh Bentall, John Beard, the anaesthetist, and Arthur Hollman, the cardiologist. There was half a ton of equipment. Four children with severe congenital heart lesions were successfully operated on, as well as two others. Melrose’s second great contribution to cardiac surgery was his introduction of a method of reversibly stopping the heart beat using cold solutions of potassium salts. In 1956 he was Nuffield travelling fellow in the USA and Fulbright fellow in 1957, becoming associate in surgery at Stanford University Medical School in 1958. Melrose was successively promoted to reader and then professor and continued to work at the Royal Postgraduate Medical School until his retirement in 1983. Melrose had the ideal temperament to lead innovative methods in medicine: exceptionally friendly and out-going, he was full of fun and at the same time exceedingly practical. In 1945 he married Ann Warter, and had two sons. His hobbies included skiing and sailing. He died in Ibiza on 2 July 2007.