Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Atrial Fibrillation

What Is It?

Atrial fibrillation is a heart rhythm disorder that causes a rapid and irregular heartbeat.

The atria are the upper two chambers of the heart that receive blood from the rest of the body. They pump blood into the lower two chambers (the ventricles). Then the ventricles pump blood to the rest of the body. During atrial fibrillation, the atria do not beat normally. Instead, they quiver or "fibrillate."

Normally, electrical impulses from a small part of the atrium called the sinus node cause the atria to beat. The electrical signal then goes through another part of the heart called the atrioventricular node. Then it goes down to the ventricles, and causes them to beat. First the atria, then the ventricles: it is coordinated, and so the heart pumps blood efficiently. The atria pump, filling the ventricles with blood, and then the ventricles pump.

In contrast, during atrial fibrillation, the electrical impulses come from all over the atria. Instead of pumping efficiently, the atria just quiver. There is an irregular and rapid heartbeat. There is no coordination between the atria and the ventricles. As a result, the atria do not pump all of their blood into the ventricles. Also, the ventricles sometimes pump when they don't have a lot of blood in them.

A normal heartbeat is 60 to 100 beats per minute, and very regular: beat…beat…beat…beat. During atrial fibrillation, the heart beats at 80 to 160 beats per minute, and is very irregular: beat..beat…..beat….beat.beat.beat….beat.

When the hearts beats rapidly and irregularly, it cannot pump blood out of the heart efficiently. As a result, some people get short of breath. Some people faint.

Atrial fibrillation can lead to the formation of blood clots inside the atria. This is a serious, longer-term problem. These blood clots can travel out of the heart and get stuck in an artery to the lungs (causing a pulmonary embolism), an artery to the brain (causing a stroke) or an artery elsewhere in the body.

The major factors that increase the risk of atrial fibrillation are:

• Age

• Coronary artery disease

• Rheumatic heart disease

• High blood pressure

• Diabetes

• An excess of thyroid hormones

In many people, the cause of atrial fibrillation is more serious than the fibrillation itself.

Atrial fibrillation is a heart rhythm disorder that causes a rapid and irregular heartbeat.

The atria are the upper two chambers of the heart that receive blood from the rest of the body. They pump blood into the lower two chambers (the ventricles). Then the ventricles pump blood to the rest of the body. During atrial fibrillation, the atria do not beat normally. Instead, they quiver or "fibrillate."

Normally, electrical impulses from a small part of the atrium called the sinus node cause the atria to beat. The electrical signal then goes through another part of the heart called the atrioventricular node. Then it goes down to the ventricles, and causes them to beat. First the atria, then the ventricles: it is coordinated, and so the heart pumps blood efficiently. The atria pump, filling the ventricles with blood, and then the ventricles pump.

In contrast, during atrial fibrillation, the electrical impulses come from all over the atria. Instead of pumping efficiently, the atria just quiver. There is an irregular and rapid heartbeat. There is no coordination between the atria and the ventricles. As a result, the atria do not pump all of their blood into the ventricles. Also, the ventricles sometimes pump when they don't have a lot of blood in them.

A normal heartbeat is 60 to 100 beats per minute, and very regular: beat…beat…beat…beat. During atrial fibrillation, the heart beats at 80 to 160 beats per minute, and is very irregular: beat..beat…..beat….beat.beat.beat….beat.

When the hearts beats rapidly and irregularly, it cannot pump blood out of the heart efficiently. As a result, some people get short of breath. Some people faint.

Atrial fibrillation can lead to the formation of blood clots inside the atria. This is a serious, longer-term problem. These blood clots can travel out of the heart and get stuck in an artery to the lungs (causing a pulmonary embolism), an artery to the brain (causing a stroke) or an artery elsewhere in the body.

The major factors that increase the risk of atrial fibrillation are:

• Age

• Coronary artery disease

• Rheumatic heart disease

• High blood pressure

• Diabetes

• An excess of thyroid hormones

In many people, the cause of atrial fibrillation is more serious than the fibrillation itself.