Atrial fibrillation is a change in your heart rhythm. It causes an irregular and sometimes very fast heartbeat.  An electrical impulse in your heart causes it to pump. Normally, this impulse starts in the right upper chamber of the heart (the right atrium). It then moves along a pathway to the lower chambers of the heart (the ventricles).

In atrial fibrillation, the electrical signal in the upper part of your heart is chaotic. The atrial muscles quiver. The electrical impulses reach the lower chambers of the heart irregularly. The irregularity can make it harder for your heart to pump efficiently. The heart may also beat very fast.

Common causes of atrial fibrillation are heart disease, including coronary artery disease, heart enlargement due to many years of high blood pressure, and heart failure.  It can also be caused by damage to the mitral valve, located in the heart between the upper and lower left heart chambers.

Other causes of atrial fibrillation include an overactive thyroid, pneumonia, chronic lung disease, and heavy alcohol use.   Sometimes no cause for atrial fibrillation can be found.