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Clarence Dennis Papers

Identifier: MS C 574


Dr. Clarence Dennis (1909-2003) was a pioneering heart surgeon and developer of a heart-lung bypass machine. Laboratory notes, correspondence, publications, and professional papers chronicle his surgical and research career at the University of Minnesota, the State University of New York, and the National Heart and Lung Institute.


  • 1927-2003


46.5 Linear Feet (42 boxes + audiovisual items)

Physical Location

Materials stored onsite. History of Medicine Division. National Library of Medicine

Language of Materials

Collection materials primarily in English

Access Restrictions

Collection is restricted. Portions of the collection are restricted according to HMD's Access to Health Information of Individuals policy. Contact the Reference Staff for information regarding access. For access to the policy and application form, please visit

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Biographical Note

Dr. Clarence Dennis, pioneering heart surgeon and developer of a heart-lung bypass machine, was born to Dr. Warren and Clara Dennis of St. Paul, Minnesota on June 16, 1909. After graduating from St. Paul's Central High School in 1927, Dennis attended Harvard College and earned his bachelor's degree in 1931. Dennis then pursued his medical degree at Johns Hopkins Medical School from 1931 to 1935 before returning to his home state for his surgical residency with Owen Wangensteen at the University of Minnesota at Minneapolis. Wangensteen required residents to earn additional degres, thus Dennis earned his master of science degree in 1938 and his Ph.D. two years later.

A health condition prevented Dennis from serving in the military during World War II, so he remained at the University of Minnesota in a variety of instructional and professorial positions in the Department of Surgery. Under the tutelage of the chairman, Dr. Owen H. Wangensteen, Dennis developed an interest in cardiac surgery, particularly the idea of a mechanism to bypass some cardio-pulmonary functions. In 1946 Dennis visited Dr. John H. Gibbon at Jefferson Medical School in Philadelphia; Gibbon had been working on a pump-oxygenator since 1934. The two surgeons traded ideas over the next few years as Dennis began working on similar technology with funding from the National Institutes of Health (NIH). In fact, Dennis received continual NIH funding from July 1947 until his departure from academic medicine in 1972.

Over the next few years Dennis constructed various apparatuses to provide a suitable substitute for the heart and lungs. Inspired by the success of artificial kidneys, he developed a similar machine; however, it failed to provide enough oxygenation of the blood during bypass. By 1951, Dennis and his staff had developed a pump-oxygenator which led to successful operations on nearly two dozen dogs; this success gave Dennis the confidence to try his machine on a human subject.

On April 5, 1951 Dennis, Dr. Richard Varco, and the University of Minnesota Hospital surgical staff performed the world's first open-heart surgery. The machine performed satisfactorily, but the young patient's heart defect proved to be much more severe than originally diagnosed, resulting in her death. Undaunted, Dennis and the staff tried again a few weeks later, but a technician's error led to the patient's death. However, Dennis's machine achieved its purpose, and work continued on the apparatus even after Dennis moved from Minnesota to assume the chair of the newly-created Department of Surgery at Downstate Medical Center, State University of New York (SUNY).

Spurred on by Dennis's work, Gibbon continued to pursue his own mechanism and performed the world's first successful open-heart surgery in 1953. Dennis's first successful surgery occurred two years later on June 30, 1955. He continued working to perfect his pump-oxygenator at SUNY for another fifteen years, even as the use of the device fell out of favor with heart surgeons as other apparatuses emerged.

In 1972 Dennis took over as Director of the Artificial Heart Program at the National Heart and Lung Institute (NHLI) at NIH. His main task was to study the feasibility of long-term usage of the artificial heart, resulting in a position paper for NIH. He argued in his paper that a lack of adequate staff numbers and expertise, coupled with advances in heart transplantation, would severely hamper the successful implementation of an artificial heart program. Ultimately Dennis concluded that the program was failing to utilize his expertise, so after three years Dennis left NIH for another position in the SUNY system, this time at Stony Brook.

For the next fourteen years Dennis worked at both Stony Brook and the Veterans Administration hospital at Northport. Returning to his medical roots, he conducted studies at the VA hospital on wounds and vagotomies while teaching surgical techniques at SUNY. After a long career as an educator and surgeon, Dennis retired in 1989 to his home state of Minnesota.

The retirement was short-lived, however, as he took a position as Director of the Cancer Detection Center at the University of Minnesota in 1991. There he led the program's efforts to encourage early cancer detection through regular testing and check-ups. Budgetary issues caused the termination of the program in 1996, and Dennis retired for the second and final time.

In addition to his career as a surgeon and educator, Dennis also served as an advocate for medical research, particularly during the anti-vivisection movement of the 1960s and 1970s. Because of his ground-breaking canine and human open heart surgeries Dennis was considered an expert on the necessity of animal testing for medical advancement. As president of the National Society for Medical Research (NSMR), he authored several articles and testified before Congress on the necessity of animal testing in ensuring the success of medical procedures on humans. In addition to the NSMR, Dennis was active in the American College of Surgeons, the Association for the Advancement of Medical Instruments, and the International Surgical Group.

In his spare time, Dennis was an inventor of non-medical devices as well, including a bread slicer and a draining board. The doctor and teacher passed away at his home in Minnesota on July 11, 2005, at the age of 96.

Brief Chronology

Fellow in Surgery, University of Minneapolis Hospitals
PhD student, University of Minnesota, Minneapolis
Fellow, then Instructor, Department of Physiology
Fellow in Surgery, University of Minneapolis Hospitals
Professor, Department of Surgery, University of Minnesota
Attending Surgeon and Administrative Head of Surgery, Minneapolis General Hospital
Professor, Department of Surgery, Downstate Medical Center, SUNY Health Science Center, Brooklyn, New York
Director of Surgery and Surgical Specialities, Kings County Hospital, Brooklyn
Performed two open-heart surgeries using his pump oxygenator (both operations unsuccessful)
Professor and Chair, Department of Surgery, Downstate Medical Center
Performed the world's second successful open-heart surgery
Director of Surgery, St. Johns Episcopal Hospital, Brooklyn
Surgeon-in-Chief, Kings County Hospital
Director, Division of Technological Applications, National Heart and Lung Institute (NHLI); Special Assistant for Technology, Office of the Director, NHLI
Professor of Surgery, SUNY at Stony Brook, New York
Staff Surgeon, VA Medical Center, Northport, New York
Associates Chief of Staff for Research and Development, VA Medical Center
Director, Cancer Detection Center, University of Minnesota
Died in St. Paul at age of 96 (July 11)

Collection Summary

Laboratory notes, correspondence, publications, and professional papers (46 linear feet; 1927-2003) chronicle the surgical and research career of Dr. Clarence Dennis. The papers span from his early education at Harvard College until his final years in Minnesota. The bulk of the collection documents Dennis's development of a pump-oxygenator, his research at the Veterans Administration, and his advocacy for the necessity of animal testing for medical advancement. The collection contains little in the way of personal materials.

Three series represent Dennis's work on open-heart surgery and the pump-oxygenator: Series 4: Heart-Lung Research, Series 5: University of Minnesota, and Series 6: State University of New York (SUNY) Downstate Medical Center. Series 4 consists of Dennis's schematics for his pump-oxygenator and his laboratory notebooks chronicling his clinical trials for the apparatus. Included in Volume VI, 1951 is a detailed description of Dennis's first (ultimately unsuccessful) open-heart surgery on a human patient. The other two series contain materials which illustrate Dennis's administrative and educational duties; Series 8: State University of New York (SUNY) Stony Brook / Veterans Administration Medical Center (VAMC) also contains materials of this type. Additionally, Series 8 documents Dennis's studies into how wounds heal after such procedures as vagotomies.

Dennis's work as an administrator is further represented by Series 7: National Heart and Lung Institute (NHLI) and Series 9: Cancer Detection Center (CDC), University of Minnesota. The majority of Series 7 concerns Dennis's position paper on the status of the NHLI's Artificial Heart Program and the Institute's work with the Atomic Energy Commission to provide an energy source for the artificial heart. Series 9 focuses mainly on Dennis's attempts to expand cancer detection practices at the university, but it also highlights his abilities as a facilitator.

Both Series 11: Writings and Lectures and Series 12: Professional Activities illustrate Dennis's professional development. Series 11 contains drafts, manuscripts, illustrations, and final prints for the dozens of articles written by Dennis throughout his career; the series also includes notes and drafts for lectures and talks given by him on various occasions. Several different national and international medical organizations are represented in Series 12, but the bulk of the series documents the activities of the National Society for Medical Research and its successors.

Personal material constitutes a small portion of the collection. Series 1: Personal and Biographical includes biographical articles and sketches as well as information on his early education; Series 3: Patents reflects Dennis's interest in inventing non-medical devices along with various medical apparatuses. Both Series 2: Correspondence and Series 13: Photographs contain a mixture of personal and professional materials.


Dr. Clarence Dennis (1909-2003) was a pioneering heart surgeon and developer of a heart-lung bypass machine. Laboratory notes, correspondence, publications, and professional papers chronicle his surgical and research career at the University of Minnesota, the State University of New York, and the National Heart and Lung Institute.

Physical Location

Materials stored onsite. History of Medicine Division. National Library of Medicine


Gift of Dr. Clarence Dennis, 2003. Accession #2003-047.


Processed by
Michele Tourney, Erica Haakensen
Processing Completed
July 2008
Encoded by
Erica Haakensen
Finding Aid to the Clarence Dennis Papers, 1927-2003
Unverified Partial Draft
Michele Tourney, Erica Haakensen
July 2008
Language of description
Script of description
Language of description note
Finding aid is written in English
Edition statement

Collecting Area Details

Part of the Archives and Modern Manuscripts Collection Collecting Area

8600 Rockville Pike
Bldg 38/1E-21, MSC 3819
Bethesda MD 20894 US
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