Cardiac muscle is striated, involuntary muscle found in the heart wall. Cardiac muscle cells (or cardiomyocytes) contain the same contractile filaments as in skeletal muscle. Unlike skeletal muscle, cardiac muscle cells are smaller with a centrally located nucleus.
Nuclei - cells have a single or occasionally two centrally located nuclei.
Intercalated Discs - cells are joined together by specialized junctions called intercalated discs. They are usually unstained, but occasionally appear as thin, dark line dividing adjacent cells. The intercalated discs are perpendicular to the direction of muscle fibers. They are best seen when stained with phospho-tungstic acid (MH 056 Muscle Types).
Lipofuscin Pigment - residue of lysosomal digestion that accumulates as yellow-brown granules near the nucleus of some cells.