BACKGROUND: Early diagnosis and proper therapy of malfunctioning prosthetic heart valves remain a challange. Transthoracic echocardiography(TTE) is the diagnostic procedure of choice for the evaluation of malfunctioning prosthetic heart valves. Howerver, TTE may be limited owing to poor acoustic windows. Some of these limitations can be overcome by transesophageal echocardiography(TTE). METHODS: The study comprised 33 consecutive patients(20 male and 13 famale patients, age range 20 to 59) in congestive heart failure after remote mitral valve replacement with bioprosthesis. The patients were examined between 1987 and 1994. All the 33 patients were studied by TTE and 19 patients among these patients furthermore by TEE. The morphology of the explanted bioprosthesis was confirmed by surgery in all cases. RESULTS: The abnormalities of the bioprosthesis were diagnosed correctly by TTE in 32 cases. The more detailed morphology of the valves could be observed by TEE(19 cases). Only in one case a small thrombus in left atrium was overlooked in TTE examination, on the otherhand it was detectedd by TEE. The severity grade of mitral regurgitation was estimatedca. I' severer by TEE in 8 cases. In all TEE examination spontaneous echocontrast was observed in left atrium. The bioprostheses from CE(Carpentier-Edwards) showed higher tendency to cuspal tearing and perforation. CONCLUSION: TTE is the diagnostic procedure of choice on patients with bioprosthetic mitral valve replacement. TTE examination confirms immediately clinical diagnosis of bioprosthetic failure. The transesophageal approach promises more detailed informations about lesions of the degenerated bioprosthetic valves and left atrium.