1. A method for assisting in determination of the suitability of a patient for a scan of a heart of the patient in a resting phase of only one cardiac cycle of the patient's heart using an X-ray computer tomograph, the method comprising: recording an electrocardiogram of the patient; evaluating, by a processor, the electrocardiogram by predicting an occurrence time of at least an immediately following R wave based upon at least four immediately consecutive R waves of the electrocardiogram which were previously measured; comparing, by the processor, the occurrence time with an actual measured occurrence time of the next R wave to obtain an accuracy of the prediction; determining, by the processor, a quality of the prediction by comparing the accuracy with a threshold; and displaying, by the processor, the quality of the prediction.