Abstract: The success of slice-followed magnetic resonance coronary angiography is dependent on how accurately the motion of the arteries can be determined as a function of respiratory position. We have measured the correction factors relating the motion of the heart to that of the diaphragm in 3 orthogonal directions with both breath-holding and free-breathing techniques, showing large variations in all three factors between subjects. We have also shown that there are large variations in the factors calculated from breath-holding and free-breathing studies within the same patient, with breath-holding factors generally being higher. This has important consequences for the quality of slice-followed acquisitions as the majority are acquired during free-breathing, with the correction factor implemented either being assumed to be fixed for all patients or having been determined through breath-holding acquisitions.