In summary, reference values of Doppler gradients obtained in a large number of patients with normal-functioning mitral and aortic Monostrut Björk-Shiley prostheses are reported. It is shown that the value of the transprosthetic gradient increases with decreasing valve size in patients with aortic prostheses. No individual significant variations of the transprothetic Doppler gradient during a 3-year follow-up were observed.