Ventricular fibrillation is a type of abnormal heart rhythm (arrhythmia). During ventricular fibrillation, disorganized heart signals cause the lower heart chambers (ventricles) to twitch (quiver) uselessly. As a result, the heart doesn't pump blood to the rest of the body.

Ventricular fibrillation is an emergency that requires immediate medical attention. It's the most frequent cause of sudden cardiac death.

Emergency treatment for ventricular fibrillation includes cardiopulmonary resuscitation (CPR) and shocks to the heart with a device called an automated external defibrillator (AED). Medications, implanted devices or surgery may be recommended to prevent episodes of ventricular fibrillation.


Collapse and loss of consciousness is the most common symptom of ventricular fibrillation.

Warning signs and symptoms

Before a ventricular fibrillation episode, you may have signs and symptoms of an abnormally fast or erratic heartbeat (arrhythmia). These warning signs may include:

  • Chest pain
  • Very fast heartbeat (tachycardia)
  • Dizziness
  • Nausea
  • Shortness of breath

When to see a doctor

Make an appointment with a heart doctor (cardiologist) if you have an unexplained, fast or pounding heartbeat.

If you see someone collapse, seek emergency medical help immediately. Follow these steps:

  • Call 911 or your local emergency number.
  • If the person is unconscious, check for a pulse.
  • If no pulse, begin CPR to help keep blood flowing through the body until an automated external defibrillator (AED) is available. The American Heart Association recommends hands-only CPR. Push hard and fast on the person's chest — about 100 to 120 times a minute. It's not necessary to check the person's airway or deliver rescue breaths. Continue until emergency medical help arrives.
  • Use an AED as soon as it's available. Deliver a shock following the prompts on the device.


To understand how ventricular fibrillation occurs, it may be helpful to know how the heart normally beats.

The normal heartbeat

Your heart is made up of four chambers — two upper chambers (atria) and two lower chambers (ventricles).

The heart's rhythm is normally controlled by a natural pacemaker (the sinus node) in the right upper chamber (atrium). The sinus node sends electrical signals that normally start each heartbeat. These electrical signals move across the atria, causing the heart muscles to squeeze (contract) and pump blood into the ventricles.

Next, the signals arrive at a cluster of cells called the AV node, where they slow down. This slight delay allows the ventricles to fill with blood. When the electrical signals reach the ventricles, the lower heart chambers contract and pump blood to the lungs or to the rest of the body.

In a healthy heart, this heart signaling process usually goes smoothly, resulting in a normal resting heart rate of 60 to 100 beats a minute.

The heart during ventricular fibrillation

Ventricular fibrillation is caused by either a problem in the heart's electrical properties or by a disruption of the normal blood supply to the heart muscle. Sometimes, the cause of ventricular fibrillation is unknown.

Risk factors

Things that may increase your risk of ventricular fibrillation include:

  • A previous episode of ventricular fibrillation
  • A previous heart attack
  • A heart defect you're born with (congenital heart disease)
  • Heart muscle disease (cardiomyopathy)
  • Injuries that cause damage to the heart muscle, such as being struck by lightning
  • Drug misuse, especially with cocaine or methamphetamine
  • A severe imbalance of potassium or magnesium


Without immediate treatment, ventricular fibrillation can cause death within minutes. The condition's rapid, erratic heartbeats cause the heart to abruptly stop pumping blood to the body. Your blood pressure drops suddenly and significantly. The longer the body lacks blood, the greater the risk of damage to your brain and other organs.

Ventricular fibrillation is the most frequent cause of sudden cardiac death. The risk of other long-term complications depends on how fast you receive treatment.

June 02, 2021
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