Cardiac rhythmicity is the spontaneous

depolarization In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is ess ...

and

repolarization In neuroscience, repolarization refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential which has changed the membrane potential to a positive value. The repolarizat ...

event that occurs in a repetitive and stable manner within the cardiac muscle. Rhythmicity is often abnormal or lost in cases of cardiac dysfunction or

cardiac failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...

. It is the ability of the heart to maintain a relatively stable relation between its systole and

diastole Diastole ( ) is the relaxed phase of the cardiac cycle when the chambers of the heart are re-filling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventri ...

. Not increasing one on the expense of the other. However, external factors may lead to the disruption of the heart's rhythmicity.

References

* PhysioEx 6.0 by Peter Zao, Timothy Stabler, Greta Peterson, Lori Smith Cardiac electrophysiology {{circulatory-stub