Following the increasing number of patients with heart valve replacement and an extended indication (older age groups, acute infective endocarditis, multivalvular procedures) the indicence of malfunction of valve prostheses is continuously growing. The prognosis of patients with a malfunctioning prosthesis mainly depends on early diagnosis and adequate therapy. In a retrospective study (1970 to 1984) 3,533 implanted heart valve prostheses were followed up and the cases with malfunction (n = 150; 4.2%) were analyzed. During the follow-up period after 1963 mitral valve replacements (MVR) there were 78 cases of malfunction (4.6%), after 1806 aortic valve replacements (AVR) 73 (4.1%), and after 34 tricuspid valve replacements (TVR) 4 malfunctions (11.8%). These malfunctions concerned periprosthetic leakages (n = 65), prosthetic endocarditis (n = 42), prosthetic valve thrombosis (n = 13), mechanical dysfunction including bioprosthetic degeneration (n = 17), valve related hemolysis (n = 3), and unsatisfactory hemodynamics (n = 10). Special attention was turned to the problem of prosthetic endocarditis (1963-1984) found in a total of 71 patients following 3,878 prosthetic valve replacements (1.9%). In 42 reoperated cases (1970-1984) the causing microorganisms were analyzed, demonstrating staphylococci in a leading position. Secondary complications and additional risk factors are discussed. There has been no change concerning the basis and the strategy of management for prosthetic endocarditis for many years: After a short time of conservative management with tested antibiotics, early reoperation and exchange of the prosthesis seems to be the optimal therapy, despite a distinctly high postoperative mortality (17%).(ABSTRACT TRUNCATED AT 250 WORDS)