After general remarks on the flow behaviour in blood circulation some experiments are described which were carried out on models in the Aero dynamischen Institut at the TH Aachen. In artery branchings, especially in prostheses, the sedimentation of substances which cause a stenosis can become critical because of secondary flows. Results obtained up to now are described on the variations of the unsteady flow conditions caused by the elasticity of the artery walls, as well as on the possibility and the danger of gas separation induced by the flow and wave phenomena. On models of artificial...