A non-invasive method for assessment of Björk-Shiley mitral and aortic heart valve movements has been developed. The Björk-Shiley tilting disc valve is described and its placement within the heart is explained. Twenty patients have been studied post-operatively with 23 valves, 10 mitral valves and 13 aortic valves, three patients having both. The method of assessment is described and consists of projecting the valve with its opaque disc marker in true profile and en face using the C arm screening system of a C.G.R. Angiorama coronary angiography unit. A cineradiograph is taken and the maximum opening angle of the valve is measured from the projected image directly or calculated from measurements taken from the image. Movement of the valve ring can also be assessed when paraprosthetic leak is suspected. The results of the study show that: (1) This method is simple, non-invasive, requires no preparation and is reproducible. (2) The valve discs open to a smaller angle than expected in most cases, and in only a few cases to 60 degrees or more. (3) It is valuable to record valve function post-operatively so that a comparison can be made later should valve malfunction be suspected. (4) In only one case was it found impossible to assess valve movement because of orientation of the valve within the patient.