1. A device for the three-dimensional reconstruction of the flow conditions in a vascular system ( 3 ) with the aid of two-dimensional projections of the vascular system during a contrast-medium injection, comprising an imaging device ( 1 ) for producing two-dimensional projection pictures of the vascular system ( 3 ) taken from different directions (A, B i , C); an injection device ( 5 ) for the controlled injection of a contrast medium into the vascular system ( 3 ); a control unit ( 6 ) that is coupled to the imaging device ( 1 ) and that is designed to drive the imaging device in accordance with the following steps: a) production of projection pictures taken from the same projection direction (A) at a high picture-taking rate during the inflow of the contrast medium after a contrast-medium injection; b) rotation of the imaging device around the vascular system ( 3 ) and production of projection pictures taken from different directions (B i ) while the vascular system ( 3 ) is filled with contrast medium.