Automaticity
In the myocardium, automaticity is the ability of the cardiac muscles to depolarize spontaneously, i.e. without external electrical stimulation from the nervous system. This spontaneous depolarization is due to the plasma membranes within the heart that have reduced permeability to potassium (K+) but still allow passive transfer of calcium ions, allowing a net charge to build. Automaticity is most often demonstrated in the sinoatrial node (SA node), the so called "Pacemaker of the Heart." Abnormalities in automaticity may result in rhythm changes.
Read more about this topic: Cardiac Action Potential