The normal heartbeat begins with electrical impulses from the sinoatrial or SA node - a group of specialized pacemaker cells in the right atrium. These impulses cause the atria to contract and push blood into the ventricles. The impulse travels down to a junction called the atrioventricular or AV node. It then moves to the ventricles, which contract and pump blood out to the lungs and the rest of the body. In people with atrial fibrillation, a chaotic electrical signal in the upper part of the heart produces a change in heart rhythm. The atrial muscles quiver. Electrical signals to the lower chambers of the heart are irregular, so that the heartbeat may be fast and irregular, and the heart may have more trouble pumping efficiently.
