An arrhythmia is an irregular heartbeat. It means your heart is out of its usual rhythm.

It may feel like your heart skipped a beat, added a beat, or is "fluttering." It might feel like it’s beating too fast (which doctors call tachycardia) or too slow (called bradycardia). Or you might not notice anything.

Arrhythmias can be an emergency, or they could be harmless. If you feel something unusual happening with your heartbeat, get medical help right away, so doctors can find out why it's happening and what you need to do about it.

There are several categories of arrhythmia, including:

• bradycardia, or a slow heartbeat;

• tachycardia, or a fast heartbeat;

• irregular heartbeat, also known as a flutter or fibrillation;

• early heartbeat, or a premature contraction.

Most arrhythmias are not severe and do not cause complications. Some, however, can increase the risk of stroke or cardiac arrest.

A normal heartbeat:

Doctors identify a healthy heartbeat by counting the number of times the heart beats every minute (bpm) during rest. This is known as the resting heart rate.

The range for a healthy resting heart rate varies between individuals, but the American Heart Association (AHA) suggests that it is usually between 60 and 100 bpm.

The fitter a person is, the lower their resting heart rate becomes. Olympic athletes, for example, have a resting heart rate of less than 60 bpm, because their hearts are highly efficient.

The heart should beat with a regular rhythm, consisting of double “ba-bum” beats with even spaces in between each.

One of these beats is the heart contracting to provide oxygen to blood that has already circulated, and the other involves the heart pushing oxygenated blood around the body.

A person can measure the heart rate using their pulse. This is a point at which they can feel the heartbeat through the skin. The best locations on the body for this are:

• the wrists;

• the insides of the elbows;

• the side of the neck;

• the top of the foot.