Cardiac arrhythmia (commonly called irregular heartbeat) is the name for a number of conditions, where the heartbeat is not normal. It may be too fast (tachycardia); too slow (bradycardia); or the heart may not beat in its regular rhythm.
Images for kids
Normal sinus rhythm, with solid black arrows pointing to normal P waves representative of normal sinus node function, followed by a pause in sinus node activity (resulting in a transient loss of heart beats). Note that the P wave that disrupts the pause (indicated by the dashed arrow) does not look like the previous (normal) P waves — this last P wave is arising from a different part of the atrium, representing an escape rhythm.
Cardiac arrhythmia Facts for Kids. Kiddle Encyclopedia.