Fluctuation analysis for the length of a single sarcomere in a myocyte in an in vivo mouse heart at rest. (A) Confocal image showing a myocyte expressed with α-actinin-AcGFP in Z-disks in the left ventricle of the heart at rest in a mouse (with greater than ∼5% isoflurane). The sarcomere within the yellow-outlined rectangle (indicated by the arrowhead) was analyzed. Scale bar, 10 µm. See Video 1. (B) Time course of changes in SL. Imaging was performed at 100 fps. (C) Histogram showing the variance of SL. Average SL, 2.260 ± 0.011 µm, indicating that the SD (i.e., index of spatial resolution) was 11 nm.