Light microscopy of a longitudinal section of cardiac muscle. The unique features of heart muscle are: a central nucleus in the cell, adjacent cells linked with branching, and cells joined end to end by specialized tight junctions. These are noted as thin vertical densities (called intercalated discs) and allow electrical communication between cells, thus facilitating coordinated heart muscle contractions. Note the muscle is striated. Capillaries and fibroblasts separate some muscle fibres. Magnification x400 when printed at 10 cm.