Left ventricular midwall function is increased after repair of coarctation of the aorta (CoA). The cause is unclear. This study aimed to examine the variance between fiber shortening derived from 3-dimensional models of myocardial deformation, and 1- and 2-dimensional indices of left ventricular systolic function. In all, 15 young adults after CoA and 15 matched control subjects were recruited. Endocardial and midwall fractional shortening were calculated using M-mode echocardiography. Ejection fraction, midwall fractional shortening, and myocardial deformation were calculated or measured from magnetic resonance (MR) imaging. Echocardiographic and cine-MR imaging midwall fractional shortening were increased after CoA (P = .02 and < .001). In contrast, 3-dimensional MR tagging demonstrated normal midwall circumferential shortening and decreased longitudinal shortening in the CoA group (P < .01). Cine MR midwall shortening, recalculated to allow for through-plane motion, was similar to tagged midwall shortening, with no difference between the CoA and control groups. After CoA, measures of left ventricular function systematically overestimate midwall fiber shortening unless the methodology accounts for through-plane motion.