Atrial Fibrillation

Normal Rhythm
Normally, the heart begins to beat when it receives an electrical prompt, causing the muscle to contract. During a normal heartbeat, an electrical signal begins in the right atrium (upper chamber of the heart) in the sinoatrial node (SA node) and travels at the same time to the left atrium and down the interatrial septum to the atrioventricular node (AV node). The impulse slows for a short time at the AV node (the bridge between the atria and ventricles) and then continues down a common pathway splitting off into the left and right bundle branches located in both ventricles.
The heart's regular pattern of electrical impulses causes the heart to fill with blood and contract in a normal fashion. This cycle of electrical activity is known as normal sinus rhythm (NSR), which describes an organized coordination between the atria and the ventricles (lower chambers of the heart), producing the familiar (lub-dub) heart sound.

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Atrial Fibrillation
Atrial Fibrillation (AF), one of the most common irregular heart rhythms, is caused when the normally regular contractions of the atria (upper chambers of the heart) are replaced by rapid and random twitching, resulting in irregular and usually faster than normal contractions (or fibrillation) of the ventricles (lower chambers of the heart).
The atria are not able to contract in a normal rhythm because the electrical signals are moving through in a in an uncontrollable fashion. The result is an irregular heartbeat, which ranges from about 50 to 150 beats per minute.

Causes

The most common cause of atrial fibrillation is aging. It occurs as we develop scarring on the upper chambers of our heart. While in many cases, the causes are not known, doctors have identified abnormalities in the heart valves and family history as contributors to atrial fibrillation.

Health conditions associated with atrial fibrillation include:

Symptoms of Atrial Fibrillation

Most patients report feeling a "fluttering" in their chest or a feeling that their heart was "skipping a beat". These are signs of an arrhythmia, or an abnormal or irregular heartbeat. Arrhythmias are extremely common, however, certain types of arrhythmias such as atrial fibrillation, are dangerous and require treatment and management.