An abnormal heartbeat (arrhythmia) is any variation in the normal heartbeat. Abnormal heartbeats occur when the heart has an irregular heart rhythm, beats too fast (tachycardia), or beats too slow (bradycardia).

The electrical system of the heart creates signals that trigger the heart to pump. These electrical signals control the heart rate and rhythm. Normally, the heart beats in a regular rhythm and at a rate that is appropriate for the work the body is doing. An arrhythmia results from a problem in the electrical system of the heart.