An arrhythmia is an abnormal heartbeat that may be unusually fast (tachycardia) or unusually slow (bradycardia). It may be related to a previous heart condition (e.g., damage from a heart attack) or to other factors (e.g., caffeine, stress, medications).

In the majority of cases, a skipped beat is not medically significant. The most serious arrhythmias, however, contribute to almost 500,000 deaths in the United States each year according to the American Heart Association, with annual deaths attributable to the condition rising steadily. Also, one type of arrhythmia called ventricular fibrillation causes most of the 330,000 sudden cardiac deaths that occur each year. Other kinds of arrhythmias contribute to stroke and the formation of blood clots.

Diagnosing an arrhythmia is very important, because the longer an arrhythmia lasts without detection or treatment,  the greater the chances of permanent damage and additional heart dysfunction. Diagnosis may be done through noninvasive tests such as an EKG (electrocardiogram) or an event monitor, or it may be done through a more invasive test such as an electrophysiology study.

Most nonsustained (temporary) arrhythmias need no treatment, although a physician may recommend certain lifestyle changes. When arrhythmias do require treatment, it may include medications, cardioversion, a catheter ablation, and/or surgery to implant either a pacemaker or an implantable defibrillator (ICD).