Atrial fibrillation (also known as AF or AFib) is the most common type of arrhythmia (irregular heartbeat or heart rhythm). The most common symptom of AF is heart palpitations (an irregular and rapid heartbeat, typically experienced as a rapid thumping in the chest). Often, the cause of AF is not known.

What is known is that AF occurs when the electrical signals of the heart are abnormal and become disorganized and very rapid. This is a result of damage to the heart's electrical system.

Usually, the damage is a result of other medical conditions, such as high blood pressure (the most common of the known causes), coronary artery disease, heart failure, or hyperthyroidism (overactive thyroid), that affect the health and function of the heart. In some instances, these causes of AF are preventable and reversible, meaning addressing these underlying causes (e.g., treating heart failure or hyperthyroidism) may prevent the development or recurrence of AF.

However, other medical conditions are not the only causes of AF. For some people, there may appear to be no obvious cause.

There are some risk factors and conditions that may put you at increased risk for atrial fibrillation. To learn if you are at risk for atrial fibrillation, read "Who is at risk for atrial fibrillation?"