SUMMARY600 patients have undergone posthetic valve replacement using the Bjork‐Shiley valve at A.I.I.M.S. between October, 1974 and June, 1983. In 400 patients cine fluororadiography has been performed and the opening angle of the disc was measured in all these cases by the method described by Venkataramanet alin 1980. Of the 400 patients, 88 had follow‐up of less than 6 months, and the rest between 6 months and 72 months. Thrombosis of the prosthetic valve was diagnosed by plain cine only in 11 cases and all cases showed restriction of movement with an opening angle less than 40° or no movement at all. All 11 cases were re‐operated and thrombectomy only was done. One patient died and the remaining ten patients are under serial plain cine review at intervals of 3 months showing normal movements to the present.Serial cine fluororadiography is a simple, inexpensive and reliable non‐invasive technique for detection of early thrombosis of Bjork‐Shiley prosthe