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Since the first months of 1955 more than 200 patients at the University of Minnesota Hospitals have undergone direct-vision intracardiac surgery, utilizing a bubble oxygenator (DeWall, Warden, Read, Gott, Ziegler, Varco, and Lillehei, 1956;Lillehei, DeWall, Read, Warden, and Varco, 1956) in combination with a pump for supporting the systemic circulation during this interval when the heart and lungs are totally by-passed.During this period of clinical experience this pump-oxygenator has passed through several stages of evolution, each design being more simple than its predecessor. All models have been constructed of expendable polyvinyl tubing and have employed the same principles of a vertical mixing tube, an antifoam-coated debubbling chamber, and a helix settling chamber for the final elimination of all bubbles. Our clinical experience with these models has been most encouraging. In order to facilitate the widest application of these advantages of open heart surgery, experiments have continued with the object of providing an equally effective and inexpensive oxygenator which also would be expendable and adaptable to commercial manufacture in quantity. THE SHEET OXYGENATORUsing the same tested principles as mentioned above, an oxygenator (Figs. 1, 2, and 3) has been developed. It is constructed of two thin sheets of polyvinyl plastic, the desired channels and chambers being delineated by a heat seal of the plastic sheets.This oxygenator is a self-contained unit with an oxygen disperser, heat sealed in the lower end of the * National Heart trainee, U.S.P.H.S.

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