Atrial fibrillation (also known as AF or AFib) is the most common type of arrhythmia (irregular heartbeat or heart rhythm). Many people are not aware of what atrial fibrillation is and refer to this heart rhythm problem as "heart flutter" or "irregular heartbeat." They may also call it "heart palpitations," which are the most common symptom of atrial fibrillation.

To understand atrial fibrillation, you need to understand how the heart works and what a normal heartbeat is.

The normal heart

The heart is a muscle made up of 4 chambers: 2 atria (the left atrium and the right atrium, making up the top half of the heart) and 2 ventricles (left and right, making up the bottom half of the heart). The heart has its own electrical system that controls the rate and rhythm of the heartbeat. The heart beats at an average of 60 to 100 times per minute at rest. The role of the heartbeat is to pump blood around the body. Blood flows into the atria, then from the atria into the ventricles, and then it is pumped out of the ventricles into the body.

The heart's electrical system signals the chambers of the heart to work in coordination to expand and contract to pump blood into the heart and out to the rest of the body. This starts with an electrical signal sent out by a group of cells called the sinus or sinoatrial (SA) node, the natural pacemaker of the heart. The SA node is located in the right atrium. From the SA node, the electrical signal travels through the right and left atria, causing the atria to contract and pump blood into the ventricles.


Figure 1

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The electrical signal then moves down to a group of cells called the atrioventricular (AV) node. The AV node is the "gateway" between the atria and the ventricles. At the AV node, the electrical signal slows down to allow the ventricles time to finish filling with blood from the atria. From the AV node, the electrical signal travels through the right and left ventricles, causing the ventricles to contract and pump blood out to the rest of the body. After contracting, the ventricles relax and the heartbeat process starts again in the SA node.

The normal heartbeat is called "normal sinus rhythm" because the SA node is controlling the electrical system of the heart.

Atrial fibrillation

In atrial fibrillation, arrhythmia (irregular heartbeat or heart rhythm) occurs because the electrical signal controlling the heartbeat becomes confused, and the atria quiver rapidly and unevenly, changing the constant rhythm of the heart.

The atria and ventricles no longer work in a coordinated way to contract and pump blood, the heart may not pump blood efficiently, and the heart rhythm becomes abnormal. In AF, the heart beats about 100 to 175 times per minute.

In our Human Atlas, you can see a video on atrial fibrillation.

It's important not to confuse atrial fibrillation with another type of arrhythmia called atrial flutter. In atrial flutter, the atria "flutter" and contract at a very rapid rate but at a regular rhythm. The electrical signals are not chaotic and irregular, as it is in AF. Sometimes atrial flutter develops into AF and sometimes AF develops into atrial flutter.

Atrial fibrillation is a serious condition that has serious complications and it can greatly affect your quality of life. AF can lead to stroke, heart failure, and hospitalizations.

The good news is that AF is manageable and most people with AF can lead active, healthy, normal lives with appropriate treatment.