A method is disclosed for assisting in determination of the suitability of a patient for a scan of the heart of the patient using an X-ray computer tomograph. In at least one embodiment of the method, a) an electrocardiogram of the patient is recorded; b) the electrocardiogram is evaluated by predicting the occurrence time of at least the immediately following R wave on the basis of at least four immediately consecutive R waves of the electrocardiogram which were measured last, and comparing this with the actual measured occurrence time of the next R wave; and c) wherein the quality of the prediction is visualized qualitatively. Further, in at least one embodiment, a device is disclosed including an ECG instrument and a computation device for carrying out the method. At least one embodiment of the invention furthermore relates to a method and a device for scanning the heart of a patient on the basis of a prediction of R waves.