A method and a CT unit are disclosed for taking cardio X-ray CT pictures, in the case of which a synthetic clock signal is used to display a clock, during each cycle phase of the synthetic clock signal. Test volume data records of the heart are reconstructed at a number of different phase instants of the synthetic clock over the complete scan, which are respectively associated with their phase instants and their z-position. Subsequently, a correlation calculation between test volume data records that are temporally neighboring and spatially identical or at least belong to the same slice plane are used to determine maxima of the correlation. Finally, imaging volume data records are subsequently calculated from the spatiotemporally associated detector data.