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 .