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Papers of Clarence Dennis Added to the National Library of Medicine’s Profiles in Science Web Site

Pioneering Surgeon Developed One of First Heart-Lung Bypass Machines


The National Library of Medicine, the world's largest medical library and a component of the National Institutes of Health, announces the release of an extensive selection from the papers of American surgeon Clarence Dennis (1909-2005), who developed one of the first heart-lung bypass machines, on the Library's Profiles in Science® Web site (//

With this addition, the number of prominent researchers, public health officials and promoters of medical research whose personal and professional records are presented on Profiles has grown to 32.

"Clarence Dennis's creative vision and rigorous research brought us one of the most important medical technologies of the 20th century," said Donald A.B. Lindberg, MD, Director of the National Library of Medicine, "Most cardiac surgery would be impossible without the heart-lung machine."

Dennis was born in St. Paul, Minnesota, on June 16, 1909. An outstanding student, he had hoped to become an engineer, but was persuaded by his mother to become a doctor like his father (who had died from pneumonia in 1923.)  Dennis received his BS from Harvard College in 1931 and his MD from the Johns Hopkins School of Medicine in 1935. He then returned to Minnesota to do an internship and surgical residency with noted surgical pioneer Owen H. Wangensteen at the University of Minnesota Hospital. There Dennis fell in love with surgical research, rapidly winning recognition for his meticulous experiments. He earned an MS in physiology in 1938, and a PhD in surgery in 1940. He then joined the faculty at the University of Minnesota, becoming full professor in 1947.

Dennis's earliest surgical research focused on intestinal conditions, including intestinal obstruction, appendicitis, and ulcerative colitis. He worked closely with Wangensteen to elucidate the origins of appendicitis, and devised many innovative surgical techniques and procedures for other conditions. Mechanically talented, he also invented devices for surgery and surgical research, which led Wangensteen to suggest, in 1945, that Dennis develop a heart-lung machine. Surgeons were then just beginning to attempt repairs to the heart, an organ long believed to be "off limits" to surgical intervention. Only a few types of repairs could be made without stopping the heart, however; to really get into the heart would require a machine that could temporarily circulate and oxygenate the patient's blood. The idea captivated Dennis, and he began his research by talking to John H. Gibbon, who had been working on a pump-oxygenator since about 1934. The two became friends, exchanging ideas and information about their parallel projects as they struggled with the many technical challenges of mechanical heart-lung devices. In April 1951, after numerous trials with dogs, Dennis and his team became the first to use a pump-oxygenator to perform open heart surgery on a human patient. The machine performed very well, but the surgeons were unable to save the young patient, whose heart defect was much more extensive than expected. Dennis's second attempted open heart operation, several weeks later, also failed, when a technician's error caused a fatal air embolism. In 1955, with an improved machine, Dennis completed the first successful cardiac operation with his machine, two years after John Gibbon's first clinical success in 1953.

While perhaps best known as a surgeon and inventor, Dennis was also a dedicated medical educator and administrator whose trainees went on to expand the boundaries of the surgical treatment of heart disease. After eleven years on the surgical faculty at Minnesota, he chaired the department of surgery at the State University of New York's Downstate Medical Center in Brooklyn from 1951 to 1971, building the department and developing residency and research programs. In 1972, Dennis retired from SUNY, and served for three years as director of the Artificial Heart Program at the National Institutes of Health. He returned to academic medicine in 1975, joining the surgical faculty at the SUNY medical school at Stony Brook. He was briefly retired again from 1988 to 1991, and then, in his early 80s, served as director of the Cancer Detection Center at the University of Minnesota until 1996.

Clarence Dennis was an active member of many professional societies for much of his career, including the American College of Surgeons and the National Society for Medical Research. Working with such groups, he helped to set standards for surgical education and ethics, shape amendments to the federal Food, Drug, and Cosmetic Act (to regulate the growing number of biomedical devices on the market), and defend the use of animals in medical research.

Profiles in Science features digitized correspondence, published articles, notebook excerpts, drafts of reports, and photographs from the Clarence Dennis Papers at the National Library of Medicine. Visitors to the site can view, for example, Dennis's letters to his family and professional colleagues, laboratory notebooks from his early experiments with the heart-lung machine, and correspondence relating to his work with the National Society for Medical Research. The site also includes correspondence and reports from Dennis's tenure as Director of the Artificial Heart Program, and photographs documenting his life and career. 

 Clarence Dennis

Shown in this undated photo, Dr. Clarence Dennis invented one of the first heart-lung bypass machines, and, in 1951, was the first to use such a device to perform cardiac surgery.