SATISFACTORY prosthetic mitral and aortic valves became generally available in 1961, and since that time the valves have been utilized in many thousands of patients with congenital or acquired valvular heart disease. Surgeons may expect, therefore, to encounter increasing numbers of patients in whom prosthetic valves have been previously implanted and in whom another illness necessitates additional operative treatment. When an abdominal or thoracic operation must be performed upon a patient with a prosthetic valve, however, special methods of preoperative, operative, and postoperative management are required. Secondary operative procedures have been carried out in 33 patients in whom one or more prosthetic cardiac valves has been inserted at the National Heart Institute. The experiences with these patients and the methods of management employed are described in the report which follows. Patients and Results Prosthetic cardiac valves of the caged-ball type have been utilized in this clinic for replacement of one