Transmission electron micrograph (TEM) of the ultrastructure of several cardiac muscle cells (cardiomyocytes) in longitudinal view showing the intercalated disc that structurally joins the cells end-to-end. These discs consist of adherens junctions for intercellular attachment and gap junctions for electrical coupling. Cardiac muscle cells are richly endowed with mitochondria and sarcomeres representing repeating contractile units of actin and myosin filaments. Magnification: x2,000 when width printed at 10cm.