Valve replacement is simply the exchange of one disease for another. Degeneration of bioprostheses and thrombotic obstruction of mechanical valves, other forms of prosthetic dysfunction and prosthetic valve endocarditis are the main complications leading to reoperation. Repeat valve surgery is more complex than primary surgery and therefore carries a higher mortality and morbidity, even in the hands of experienced surgeons. Several technical details of valve replacement have contributed to the improved results obtained by some surgical groups. Difficulties start with the opening of the sternum, especially in cases where the pericardium was not closed during the initial operation. Cardiopulmonary bypass may be instituted in the usual fashion or may be done by cannulation of the femoral or iliac vessels. The heart need not be completely liberated from the adhesions. Access to the aortic root is usually not difficult, but the left atrium may be less accessible. Removal of the prosthesis also requires precise technique, for disruption of the annulus or damage to other valves or neighbouring structures may occur. Finally, the choice of valve substitute and technique of implantation must be tailored to the patient's characteristics and the type of pathology. One of the most important causes of morbidity and mortality after reoperation is perioperative and postoperative bleeding, resulting from the extensive dissection and from the coagulation disorders, including anticoagulation treatment. Pharmacological manipulation has recently contributed to reduce the severity of this complication. The results of repeat valve surgery have improved markedly and have now reached values which approximate those of primary valve replacement.(ABSTRACT TRUNCATED AT 250 WORDS)