A method for generating a solid model of a heart in a predetermined phase of its periodic pumping movement is proposed. During a single C-arm rotation of a C-arm X-ray unit an electrocardiogram signal with consecutive RR intervals is observed by an EKG trigger. In each RR interval a digital X-ray image is generated by EKG triggering of the C-arm X-ray unit as soon as a time difference between the current phase and the predetermined phase is less than a predetermined value. For each of the X-ray images in addition a parameter influencing the geometry of the C-arm X-ray unit is ascertained. The solid model is generated from several of the X-ray images. At least one X-ray image is selected from each RR interval and for each of the selected X-ray images a projection data set for the calculation of the solid model is ascertained by the ascertained parameter.