Ventricular Fibrillation

The heart muscle is responsible for circulating blood throughout the body and uses electrical signals from within the heart to control the heartbeat. When the electrical system of the heart does not operate as it is supposed to, ventricular fibrillation can develop.

During ventricular fibrillation, chaotic electrical impulses to the ventricles — the lower chambers of the heart — can cause the ventricles to quiver rather than contracting in a coordinated way. No blood is pumped from the heart, causing a form of cardiac arrest that is fatal unless treated immediately.


Ventricular fibrillation causes a loss of consciousness in seconds. Without treatment, the brain doesn't get enough oxygen. A person will typically develop seizures and irreversible brain damage after approximately five minutes. Death soon follows.

Signs of cardiac arrest include:

  • Sudden loss of responsiveness
  • Not breathing or only gasping

Early signs and symptoms of ventricular fibrillation include:

  • Chest pain
  • Rapid heartbeat (tachycardia)
  • Dizziness
  • Nausea
  • Shortness of breath
  • Loss of consciousness

Causes and Risk Factors

The cause of ventricular fibrillation is not always known. The most common cause is a lack of blood flow to the heart muscle due to coronary artery disease, such as occurs during a heart attack.

Other risk factors include:

  • Drowning
  • Drugs that affect electrical currents in the heart (such as sodium or potassium channel blockers)
  • Electrical shock
  • Very low blood pressure, which can result from coronary artery disease and other disorders
  • Very low levels of potassium in the blood (hypokalemia)
  • A previous episode of ventricular fibrillation
  • A previous heart attack
  • Congenital heart disease
  • Heart muscle disease (cardiomyopathy)
  • Use of illegal drugs, such as cocaine or methamphetamine


Ventricular fibrillation is always diagnosed in an emergency situation. A diagnosis is made based on the results of heart monitoring or a pulse check.

After the patient has received immediate emergency care, diagnostic tests to determine the cause of the ventricular fibrillation will be performed. This may include tests to examine the heart muscle, the blood flow through the heart, and any potential leaking within the heart valves. An electrocardiogram (EKG) is a painless procedure that provides a picture of the electrical activity of the heart and how the heart is working. A similar test is an echocardiogram, a noninvasive procedure that uses ultrasound to create a moving picture of the heart as it works.

Additional imaging tests such as a cardiac MRI or chest X-ray may be used to see if the heart is enlarged — if the echocardiogram is inconclusive. An angiogram may be used to view the blood vessels around the heart.

Other diagnostic tests may include electrophysiology studies to look at the electrical system of the heart.


Ventricular fibrillation is an extreme medical emergency. Cardiopulmonary resuscitation (CPR) must be started as soon as possible — within a few minutes. Defibrillation (an electrical shock to the chest) should be administered. Antiarrhythmic drugs may then be given to help maintain a normal heart rhythm.

An electrical shock to the heart can restore normal heart rhythm if the ventricular fibrillation occurs within hours of a heart attack in a person who is not in shock and does not have heart failure. If shock and heart failure are present, it is likely there is major damage to the ventricles. Defibrillation is not as successful in these cases.

Once a person has been brought back from ventricular fibrillation, they are at high risk of having another episode. Treatment includes treating an underlying disorder if it is reversible and a cause of the ventricular fibrillation. Drugs may also be given to prevent reoccurrences.

Surgery to implant a defibrillator in the chest can also be performed. The defibrillator identifies abnormal heart rhythms and sends an electric shock to the heart to correct the problem.

The knowledgeable and highly trained staff at the Cedars-Sinai Heart Institute will work with each patient to determine the best treatment option.