Representative data showing SL changes in an LV myocyte in a mouse with normal systolic function. (A) Left: Confocal image of a myofibril used for the analysis of sarcomeres (enlarged view of M1 in the yellow-outlined rectangle in Fig. 1 A). Right: Same as in left image, processed by Gaussian smoothing filter (1 σ). Data on sarcomere nos. 1–6 are shown below. Scale bars, 10 µm. (B) Left: Confocal images for sarcomere nos. 1–6 at various time points (i.e., 0.42, 0.43, 0.44, 0.45, and 0.46 s from the onset of imaging; compare Fig. 1 B). Sarcomere numbers are indicated on top and time points on left. Right: Same as in left image, processed by Gaussian smoothing filter (1 σ). Plot profiles were obtained from the raw data (left). Colored lines below the plot profiles indicate individual SLs (derived based on the plot profiles). Scale bars, 2 µm. (C) Data showing time course of changes in the lengths of sarcomere nos. 1–6 (sarcomere numbers indicated on right). At the midpoint of 0.44 s, SL values were 1.90, 1.79, 1.61, 1.89, 1.70, and 2.48 µm for sarcomere nos. 1, 2, 3, 4, 5, and 6, respectively (shortest [no. 3] and longest [no. 6] sarcomeres indicated by arrows). Magnitudes of change in SL were 11.8%, 15.6%, 14.7%, 16.1%, 20.2%, and 28.7% for sarcomere nos. 1, 2, 3, 4, 5, and 6, respectively. See Video 2.