Cardiac muscle (myocardium) is striated, involuntary muscle found in the heart wall. Cardiac muscle cells (cardiomyocytes) contain the same contractile filaments as in skeletal muscle (sarcomeres). They are intermediate in size compared to skeletal and smooth muscle.
Nuclei - cardiac muscle cells have a single or occasionally two centrally located nuclei.
Intercalated Discs - cardiac muscle cells are joined together by specialized junctions called intercalated discs. They appear as thin, dark stained linear structures dividing adjacent cells that are perpendicular to the direction of the muscle fiber
Lipofuscin Pigment - residue of lysosomal digestion that accumulates as yellow-brown granules near the nucleus of some cells. In this specimen, few cells have detectable amounts.