Left ventricular (LV) long-axis shortening produces cardiac motion through fixed short-axis sections, complicating accurate quantification of myocardial and wall-motion parameters with MRI. Therefore, LV long-axis length and shortening was studied in both long- and short-axis end-diastolic (ED) and end-systolic (ES) MRI scans. A group of 38 male volunteers underwent gradient-echo cine-MRI: single-slice long-axis and multi-slice short-axis. The LV dimensions were directly measured in the long-axis images using epicardial and endocardial contours. The position of the apex and the base (aortic valve) were assessed in the sections of the short-axis scan. The LV dimensions as measured on both long- and short-axis scans showed a correlation of r = 0.62 for ED and r = 0.69 for ES. Relative LV shortening between long- and short-axis scans showed a poor correlation (r = 0.22). These results suggest that short-axis MRI is not sufficient to accurately assess through-plane motion. Therefore, long-axis images are needed for optimal quantification of myocardial and wall-motion parameters.