The contractile myocytes are arranged in distinct bundles termed fascicles. The orientation of the bundles varies between the atria and the ventricles. Standardly, there are multiple layers which blend with each other and spiral towards the apex within the ventricles.
Theoretically, the arrangement of the bundles should explain the dimensional changes within the chambers during systole e.g. the timing of atrioventricular valve closure relative to ventricular systole.
All the fascicles seem to have a common connection to the fibrous skeleton of the heart.
Last reviewed 01/2018