The architecture of the myofibril layers of the left ventricle is complex. Most of its fibers are organized circumferentially, particularly in the midwall and the base of the ventricle. There is, however, a progressive change in fiber orientation across the wall of the left ventricle, and longitudinally directed fibers prevail in the subendocardial and subepicardial free walls. In contrast to the EF, which reflects the radial/circumferential function, MAPSE measures longitudinal LV function by quantifying the displacement of the annulus toward the apex. MAPSE should be measured using M-mode ultrasonography to interrogate the septal, lateral, anterior, and posterior walls in the apical four- and two-chamber views. Systolic excursion should be measured from the lowest point at end-diastole to the maximal point at end-systole, usually corresponding to the T wave on the ECG. Reduced MAPSE is mostly related to either subendocardial ischemia or fibrosis and correlates well with EF in normal patients and in those with dilated cardiomyopathy. There is discussion in the literature as to whether individual values should be used or the mean of the walls sampled. However, a value < 6 mm for predicting a severely depressed EF has a specificity of 100% in men and 88% in women, with a sensitivity of 73% in men and 100% in women. The positive predictive value for MAPSE ≥ 11 mm in women to predict a normal EF was 94% (sensitivity, 92%). The positive predictive value for MAPSE ≥ 13 mm in men to predict a normal EF was 94% (sensitivity 92%). In ischemia, MAPSE is more sensitive than EF in detecting early abnormalities and can be readily measured in patients with poor image quality, in which EF is known to be inaccurate.