Heart muscle cells, fluorescence light micrograph. Cardiac muscle cells (cardiomyocytes) are found in the heart. Fluorescent markers have been used to highlight proteins in the cell nuclei (blue) and cytoskeleton (red and green). The proteins stained here are: actin (red) and desmin (green) to show the intermediate filaments of the cytoskeleton. These intermediate filaments are essential for the structural integrity and function of muscle. Cell nuclei have been stained with DAPI. This sample is from rat tissue.