The Doppler characteristics of Björk-Shiley Monostrut prostheses in mitral position were studied in 53 patients (35 women; 18 men; mean age 53.8 yrs). Valvular function was considered normal on the basis of clinical and echocardiographic evaluation. Mean follow-up after surgery was 23.9 +/- 12.0 months (range 9-53). M-mode, two-dimensional and colour flow mapping echo were performed in each patient. Transvalvular blood flow characteristics were examined by colour flow imaging whereas peak and mean gradient through the valve, pressure half-time and prosthetic area were calculated using continuous wave Doppler. In 84% of patients, colour flow mapping showed a transprosthetic flow with 2 jets; in 78% the jets were different: the main one was directed towards the free wall of left ventricle in 52% and towards the interventricular septum in 48%. Thus, the main jet direction was dependent on the spatial position of the prostheses and the orientation of the disc. In 16% a single jet flow was present during the whole diastole. CW Doppler showed the following parameters: peak velocity 1.6 +/- 0.3 m/s; peak gradient 10.7 +/- 3.9 mmHg; mean gradient 3.8 +/- 2.3 mmHg; pressure half-time 83.3 +/- 16.6 msec; prosthetic area 2.7 +/- 0.51 cm2. No statistically significant difference was found between different size prostheses. Our data show the excellent long term hemodynamic parameters of Björk-Shiley Monostrut mitral prosthesis and confirm the value of colour flow mapping in identifying normal transprosthetic flow profile.