The heart is a pump made of very strong muscle that beats, on average, 60 to 100 times a minute. The body's own electrical system sends impulses to the heart muscle, telling it when to pump blood. A change in the pace or pattern of your heartbeat is called an arrhythmia. Although frightening, these changes are usually not serious, unless you also have heart disease.

An arrhythmia affects the way in which your heart pumps by speeding up or slowing down the electrical impulses that tell your heart when to beat. If the arrhythmia lasts for longer than a few heartbeats, you may begin to feel lightheaded, dizzy or weak. You may also feel your heartbeat "racing" for a few beats.

To diagnose your arrhythmia, your doctor may order an electrocardiogram (ECG), which shows the pattern of your heartbeat. If your arrhythmia occurs only once in awhile, your doctor may ask you to wear a Holter monitor for 24 hours or more. If a serious arrhythmia is suspected, electrophysiologic studies may be performed. Once your arrhythmia has been diagnosed, your doctor may suggest one or more of the following therapies. The use of these therapies is dependent upon the type of arrhythmia you have.

• Medication When your heartbeat is irregular, medicine is often first to restore the rhythm of your heart. You and your doctor may have to try several drugs before you find the one that works best for you.
  
• Pacemakers Artificial pacemakers are electronic devices that can be used to replace your heart's own electric impulses to restore a normal, regular heartbeat. Pacemakers, which are surgically implanted under the skin of the chest and have wires running into the heart, are most commonly used to correct abnormally slow heart rates. The new pacemakers last for eight to 10 years before they need to be replaced.
  
• Defibrillators When patients are experiencing a potentially lethal arrhythmia (irregular heartbeat), the doctor may recommend an internal defibrillator. Like pacemakers, internal defibrillators are battery-powered electronic devices that are surgically implanted in the body to stimulate the heart, particularly for cases of ventricular tachycardia (rapid heartbeat) and ventricular fibrillation (failure of the ventricles to pump blood out of the heart). Defibrillators, which are larger than pacemakers, are often implanted beneath the skin and muscle of the abdomen. Wires used to sense the heartbeat may be inserted through veins into the inside of the heart. Other wires may be attached to the surface of the heart, to be used when a shock to the heart is required. Some defibrillators include a pacemaker. Defibrillators are also called AICDs, or automatic implantable cardiac defibrillators.