Scheme showing the protocol of experiments on cardiomyocytes. Assuming that the cardiomyocyte has the shape of an elliptic cylinder (top left), the y-axis was defined as the longitudinal axis, the x-axis as the horizontal transverse axis, and the z-axis as the vertical transverse axis. Top right, the cell from above as viewed in the confocal microscope. Bottom panels describe acquisition of raster image correlation spectroscopy (RICS) images. First, the scanning field was rotated to orient the y-axis of the scanning field in parallel with the cell's longitudinal direction. This was defined as the position with an angle of 0°. A series of images was acquired at this position with a pixel size of 0.1116 μm. The scanning field was then rotated 45°, and a new series was acquired. The scanning field was then rotated again to a total of 90° so that the y-axis of the scanning field was parallel with the cell's transverse direction, and the last series was acquired. The acquisition at different angles was repeated at pixel sizes of 0.0558 and 0.0279 μm. This procedure was performed with 3 pixel dwell times: 25, 51, and 102 μs.