The heart is like a clock. It has a regular beat which can almost be predicted, like the drum rhythm in a song. At certain times like when we are stressed or exercising this rhythm increases in speed and at others (during sleep) it slows. The order of this rhythm is usually very tightly controlled and happens in a specific order. In some people this order or the whole rhythm itself is disrupted. This is called an arrthymia or abnormal rhythm. There are many, many different types of abnormal rhythm but broadly your cardiologists will be aiming to ensure you are not at risk of any life threatening events - where you rhythm gets out of control or the heart becomes very confused it does not beat in an organised, ordered way.