Atrial Fibrillation

Atrial fibrillation is an abnormal heart rhythm. The heart's electrical system normally sends regularly spaced signals. These signals tell the heart muscle to contract or beat. The heart has two upper chambers called atria. It also has two lower chambers called ventricles. Each signal starts in the atria and travels to the rest of the heart. In atrial fibrillation, the electrical signals from the atria are fast and irregular. The atria shake instead of contract. Some signals do not reach the ventricles and the ventricles continue pumping. This pumping is usually irregular and sometimes rapid. This rhythm can reduce the heart’s ability to pump blood out to the body. Blood left in the heart chambers can form clots. These clots may sometimes break away and travel to the brain. This can cause stroke.

  • Causes

    In most cases, atrial fibrillation is due to an existing heart condition. Atrial fibrillation can also occur in people who do not have structural heart problems. A thyroid disorder or other condition may cause the abnormal rhythm. The cause of atrial fibrillation is sometimes unknown.

  • Definition

    Atrial fibrillation is an abnormal heart rhythm. The heart's electrical system normally sends regularly spaced signals. These signals tell the heart muscle to contract or beat.


    The heart has two upper chambers called atria. It also has two lower chambers called ventricles. Each signal starts in the atria and travels to the rest of the heart. In atrial fibrillation, the electrical signals from the atria are fast and irregular. The atria shake instead of contract. Some signals do not reach the ventricles and the ventricles continue pumping. This pumping is usually irregular and sometimes rapid. This rhythm can reduce the heart’s ability to pump blood out to the body. Blood left in the heart chambers can form clots. These clots may sometimes break away and travel to the brain. This can cause stroke.

    Atrial Fibrillation
    Nucleus factsheet image
    Copyright © Nucleus Medical Media, Inc.

  • Diagnosis

    The doctor will:

    • Ask about your symptoms and medical history
    • Perform a physical exam
    • Listen to your heart with a stethoscope

    You doctor will order blood tests to help diagnose the problem.

    • Your doctor may need pictures of your heart. These can be made with:
      • Chest x-ray
      • Echocardiogram
      • Coronary angiography
    • Your doctor may need to evaluate your heart function. This can be done with:
      • Electrocardiogram (EKG)
      • 24-hour Holter monitor

  • Prevention

    Avoid known triggers if you have risk factors for atrial fibrillation. Also, follow your doctor's advice for controlling chronic conditions, like heart disease and high blood pressure.

  • Risk Factors

    Factors that may increase the risk of atrial fibrillation include:

    • Age: 55 or older
    • Sex: male
    • Family history of atrial fibrillation

    • Cardiovascular diseases, such as
      high blood pressure,
      coronary artery disease,
      congestive heart failure,
      heart attack, heart valve disease,
      endocarditis,
      cardiomyopathy, congenital heart disease, prior episode of atrial fibrillation

    • Lung diseases, such as
      emphysema,
      asthma, blood clots in the lungs

    • Chronic conditions, such as
      overactive thyroid, diabetes

    • Receiving
      general anesthesia

    • Lifestyle factors, such as use of stimulant drugs (including caffeine),
      smoking,
      alcohol abuse, stress (either physical or emotional)

  • Symptoms

    Symptoms can be mild to severe. This depends on your heart function and overall health. Some people may not notice any symptoms.

    Symptoms include:

    • Irregular or rapid pulse or heart beat
    • Racing feeling in the chest
    • A pounding feeling in the chest
    • Dizziness, lightheadedness, or fainting
    • Sweating
    • Pain or pressure in the chest
    • Shortness of breath
    • Fatigue or weakness
    • Unable to exercise

  • Treatment


    The goals of treatment are to:

    • Return your heart to a regular rhythm, if possible.
    • Keep your heart rate close to normal.—Your doctor will tell you your target heart rate. In general, your resting rate should be between 60-80 beats per minute. It should be 90-115 beats per minute during moderate exercise.
    • Prevent blood clots from forming.

    Your doctor may find another condition that is causing atrial fibrillation. This condition may be treated. In some cases, heart rhythm problems return to normal without treatment.

    Treatment options include: