When observing cardiac tissue through a microscope, intercalated discs are an identifying feature of cardiac muscle. Cardiac muscle consists of single heart muscle cells (cardiomyocytes) which have to be connected by intercalated discs to work as a functional organ. By contrast, skeletal muscle consists of multinucleated muscle fibers and therefore exhibit no intercalated discs. Intercalated discs support synchronised contraction of cardiac tissue. They can easily be visualized by a longitudinal section of the tissue.

Cell biological textbooks mention three types of cardiomyocyte adhering junctions within an intercalated disc—fascia adherens

Fascia adherens

Fascia Adherens is a ribbon like structure that stabilizes non-epithelial tissue. Is similar to the Zonula Adherens or Adherens junction of epithelial cells but it's not belt-like. It's a broad intercellular junction in the longitudinal sections of an intercalated disk of cardiac muscle anchoring...

, macula adherens (aka desmosomes), and gap junction

Gap junction

A gap junction or nexus is a specialized intercellular connection between a multitude of animal cell-types. It directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells....

s.

• Fascia adherens
  Fascia adherens
  Fascia Adherens is a ribbon like structure that stabilizes non-epithelial tissue. Is similar to the Zonula Adherens or Adherens junction of epithelial cells but it's not belt-like. It's a broad intercellular junction in the longitudinal sections of an intercalated disk of cardiac muscle anchoring...
  
  are anchoring sites for actin
  Actin
  Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
  
  , and connect to the closest sarcomere
  Sarcomere
  A sarcomere is the basic unit of a muscle. Muscles are composed of tubular muscle cells . Muscle cells are composed of tubular myofibrils. Myofibrils are composed of repeating sections of sarcomeres, which appear under the microscope as dark and light bands...
  
  .

• Macula adherens stop separation during contraction by binding intermediate filaments, joining the cells together. Macula adherens junctions are also called desmosome
  Desmosome
  A desmosome , also known as macula adherens , is a cell structure specialized for cell-to-cell adhesion...
  
  s.

• Gap junctions allow action potential
  Action potential
  In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
  
  s to spread between cardiac cells by permitting the passage of ions between cells, producing depolarization
  Depolarization
  In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
  
   of the heart muscle.

However, molecular biological and comprehensive studies have shown that intercalated discs consist for the most part of mixed type adherens junctions termed composite junctions or areae compositae (singular area composita). These represent an amalgamation of typical desmosomal and fascia adherens proteins (in contrast to various epithelia) . Thus cardiomyocyte adherens junctions differ from epithelial zonula adherens and desmosomes.