To ascertain whether or not left ventricular geometry changes during preload reduction and afterload increment, the shortening characteristics of small segments in the left ventricular free wall were examined using 4 pairs of ultrasonic crystals in 10 dogs. Three pairs of ultrasonic crystals were circumferentially implanted in the basal, the midventricular and the apical portion of the left ventricle. Another pair of crystals were longitudinally placed in the midventricle. In the control state, the shortening at the apex was largest of all segments. During preload reduction, the end-diastolic length decreased significantly in each segment. The percent shortening decreased significantly at the apical and the longitudinal segment, but it remained unchanged at the midventricular and the basal segment. During afterload increment, the end-diastolic length increased significantly, but the percent shortening remained unchanged in each segment. We concluded that left ventricular geometry was altered during preload reduction and that the apical part is more responsive to preload change than the other portion.