myocardium (heart, histology)

Last reviewed 01/2018

The myocardium of the heart is the muscular component of the wall that is thicker within the ventricles than the atria. It is continuous with the tunica media of the adjoining blood vessels. Deep, it is continuous with the connective tissue of the endocardium of the heart. More superficially, it is continuous with the epicardial layer.

The myocardium can be divided into two key types of cell:

  • predominantly contractile myocytes - 'cardiac muscle':
    • forms the bulk of the atria and ventricles
    • the orientation of fibres varies between the atria and the ventricles - see submenu
    • also present in:
      • papillary muscles - specialized conical projections of the myocardium
      • trabeculae carneae
      • the atrioventricular valves as infrequent, isolated myocytes
  • myocytes adapted for conduction of electrical impulses from the pacemaker regions

Both sets of cells are suspended in a matrix of fine connective tissue. They are associated closely with a ramifying network of capillaries.