Cardiac Physiology
The heart's continuous beating is due to an inherent, rhythmical electrical activity. Autorhythmic cells make up about 1% of cardiac muscle fibres. These cells repeatedly fire spontaneous action potentials that then trigger heart contractions. This is why a heart will continue to beat even when removed from the body. Although signals from the autonomic nervous system or endocrine system can modify the heartbeat, they do not establish its fundamental rhythm.