Owen Wangensteen at the University of Minnesota in the United States had been impressed by the work of Alan Thal, a young South African doctor working in Minnesota. Wangensteen asked Groote Schuur Head of Medicine John Brock if he might recommend any similarly talented South Africans and Brock recommended Barnard. In December 1955, Barnard travelled to Minneapolis, Minnesota to begin a two-year scholarship under Chief of Surgery Wangensteen, who assigned Barnard more work on the intestines, which Barnard accepted even though he wanted to move onto something new. Simply by luck, whenever Barnard needed a break from this work, he could wander across the hall and talk with Vince Gott who ran the lab for open-heart surgery pioneer Walt Lillehei. Gott had begun to develop a technique of running blood backwards through the veins of the heart so Lillehei could more easily operate on the aortic valve (McRae writes, "It was the type of inspired thinking that entranced Barnard"). In March 1956, Gott asked Barnard to help him run the heart-lung machine for an operation. Shortly thereafter, Wangensteen agreed to let Barnard switch to Lillehei's service. It was during this time that Barnard first became acquainted with fellow future heart transplantation surgeon Norman Shumway. Barnard also became friendly with Gil Campbell who had demonstrated that a dog's lung could be used to oxygenate blood during open-heart surgery. (The year before Barnard arrived, Lillehei and Campbell had used this procedure for twenty minutes during surgery on a 13-year-old boy with ventricular septal defect, and the boy had made a full recovery.) Barnard and Campbell met regularly for early breakfast. In 1958, Barnard received a Master of Science in Surgery for a thesis titled "The aortic valve – problems in the fabrication and testing of a prosthetic valve". The same year he was awarded a Ph.D. for his dissertation titled "The aetiology of congenital intestinal atresia". Barnard described the two years he spent in the United States as "the most fascinating time in my life."