A method for simulating a blood flow in a vascular segment of a patient is proposed. A 3D image dataset of an examination region is recorded by a radiographic diagnostic device for generating a 3D vascular model. Contrast agent propagation in the examination region is captured by a dynamic 2D angiography method for generating a real 2D angiography recording. A CFD simulation of the blood flow is performed in the 3D vascular model based on a blood flow parameter for generating a virtual 2D angiography recording. A degree of correspondence between the real and the virtual 2D angiography recordings is determined from identical angulation and adjusted recording geometry of the patient and compared with predefinable tolerance values. The CFD simulation is iteratively optimized while changing the blood flow parameter as a function of the comparison. The degree of correspondence is outputted when the optimum CFD simulation is achieved.