Every year many heart patients use man-made valves which can be seriously imperiled by thrombi. The folw of the bloodstream passing through a man-made valve is one of the most important causes that bring about thrombi. The bloodstream is simulated with the help of a 10: 1 model and observed through a fluid visualization method. The dynamic process is videotaped by a videocamera. Then man can get the velocity and displacement of each small area by means of digital image processing and matching.The fluid arrow picture

that accurately describes the bloodstream in every twinkling

is obtained thereby.The quantitative description of the bloodstream is realized. With this method man can analyse the causes of thrombi

that the structure of a man-made valve leads to

and find valuable phenomena from it.