Various types of pump oxygenators are now being employed in the surgical correction of intracardiac anomalies. Certain basic physiological criteria will have to be satisfied with all such machines if the majority of such operations are to be successful. Only part of the responsibility for successful intracardiac surgery rests with the machine. The clinical management of the patient before, during, and after the operative procedure is equally important. Furthermore, new intracardiac surgical techniques have to be devised and perfected. Consequently, the problem of successful direct-vision open intracardiac surgery is threefold, and success is dependent upon the development of a reliable pump oxygenator that maintains the physiological requirements of the body, the clinical management of the patient, and the employment of a satisfactory surgical technique. The requirements of a pump oxygenator are that it must (1) provide the needs of the body for oxygen without the dangers of emboli or foaming,