Cineradiography is the most accurate and rapid method in evaluation of the function of Björk-Shiley prosthetic valves manufactured after late 1975 and which incorporate a tantalum foil hoop into the disc. This helps in demonstration of the disc and in the calculation of the opening angle of the disc. In the present series 8 cases with valve dysfunction have been correctly diagnosed by conventional cineradiography, 7 in the mitral and one in the aortic position. In all 8 cases and also in the group of 300 postoperative cases having no symptoms, the opening angle has been measured by the method described by Venkataraman et coll. in 1980. It is recommended that in accordance with the suggestions of these authors, the opening angle should be established for each patient in the immediate postoperative period in order to provide a basis for possible future examinations.