Ventricular fibrillation

Alternative names


ventricular fibrillation (VF) is a severely abnormal heart rhythm (arrhythmia) that, unless treated immediately, causes death. VF is responsible for 75% to 85% of sudden deaths in persons with heart problems.

To pump blood out to the body, all areas of the heart normally squeeze (contract) in an organized, synchronic manner. The heart’s upper chambers (the atria) contract first, and then the heart’s bottom two chambers (ventricles) contract. During VF, however, the ventricles contract independently of the atria, and some areas of the ventricles contract while others are relaxing, in a disorganized manner.

Causes, incidence, and risk factors

The most common cause of VF is a heart attack, but VF can occur whenever the heart muscle is affected by a poor supply of oxygen or by specific heart disorders.

Conditions that can lead to VF include:

  • acute or previous heart attack  
  • ischemia (lack of oxygen to the heart muscle because of narrowed coronary arteries or shock)  
  • congenital heart disease  
  • heart surgery  
  • diseases of the heart muscle, such as cardiomyopathies  
  • electrocution accidents or accidents involving direct trauma to the heart

ventricular fibrillation is the main cause of sudden cardiac death, which in turn affects nearly 300,000 people each year in the U.S.

While most people suffering from VF have no previous history of heart disease, many have risk factors for cardiovascular disease, such as smoking, hypertension, and diabetes.

The person having VF suddenly collapses or falls unconscious, because the brain and muscles have stopped receiving blood from the heart. Within one hour before the collapse (or sudden death from VF), some people complain of symptoms such as chest pain, palpitation, shortness of breath, dizziness, or nausea.

Signs and tests

The person will be unresponsive. The carotid pulse in the neck and femoral pulse in the groin may be hard or impossible to detect. When listening to the heart with a stethoscope, the heartbeats cannot be heard or they may have varying intensity and be very irregular.

If the person having VF was already in the hospital, or if paramedics have connected the person to a cardiac monitor, the monitor will show a disorganized arrhythmia (VF). The VF in turn can evolve into a flat line or cardiac arrest.


ventricular fibrillation is a medical emergency and should be treated immediately to preserve life. Whether the person having VF suddenly falls unconscious at home or in the street, or the person is in the hospital (and VF is diagnosed from a cardiac monitoring station), it is indispensable to initiate immediate Cardiopulmonary resuscitation (CPR). If VF occurs in the hospital, prompt medical attention is usually available and is more likely to be successful.

During an out-of-hospital cardiac arrest:

  • Call 911 for emergency help.  
  • Until help arrives, position the unconscious person’s head and neck in line with the rest of the body to help the person breathe.  
  • The carotid arteries are located at each side of the neck, just below each angle of the jaw. Place your fingertips on one of the carotid arteries to try to find a pulse. Not finding a carotid pulse after several attempts is usually a sign that no pulse is present.  
  • Start CPR with mouth-to-mouth breathing and chest compressions.  
  • Continue CPR until the person regains consciousness or help arrives.

Paramedics will quickly examine the person while continuing CPR. VF is treated by using an external defibrillator, which delivers a quick electric shock through the chest. The Electrical shock can immediately convert the VF into a normal rhythm. Stabilizing the heart rhythm and function may require medicines, which will be given through a vein as needed.

Once the VF has been converted to normal heart rhythm (and the patient has been transferred to the hospital, if resuscitated in the street), and to prevent further episodes of VF, the cardiologist will look for potential causes of the arrhythmia. The causes most commonly involved are ischemic heart disease and cardiomyopathies.

Expectations (prognosis)

Victims of VF may never convert to the normal rhythm, or they may die (within a few minutes or a few days of the VF) from cardiac failure or VF complications. For out-of-hospital cardiac arrest, the survival rates of VF are slim and range between 2% and 25%.

People who have survived an episode of VF are prone to have another episode, and should be evaluated by an electrophysiologist. Currently, many VF survivors are offered therapy through an implantable cardioverter defibrillator (ICD), a device that is similar to a pacemaker and that can electrically treat new episodes of VF as soon as they occur. The ICD has shown to effectively prevent sudden cardiac death.


The most common complication of VF is sudden death (death within 1 hour of the onset of symptoms), followed by death in the hospital (among people who were transferred to a hospital after being rescued at home, in the street, or in the workplace). For survivors of VF, complications include coma, reduced mental acuity, and neurological problems similar to those seen after a stroke.

The neurological status of patients with coma after resuscitation from out-of-hospital cardiac arrest can apparently be improved with the use, in the hospital, of moderate hypothermia (i.e., low body temperature).

Calling your health care provider

If someone is having VF, paramedics should called immediately at 911.

After surviving an episode of VF, your doctor should be informed as soon as possible so that cardiac treatment and prevention can be coordinated for you.


Patients who have had an episode of VF may prevent further VF episodes with an ICD. For other patients, it may be more advisable to initiate preventive therapy with antiarrhythmic drugs.

People who have ischemic heart disease may be offered treatment aimed to restore normal oxygenation to the heart muscle, thus preventing arrhythmias. Patients with cardiomyopathies may require special procedures, including cardiac transplantation.

Some public places like casinos and commercial aircraft are now equipped with automated external defibrillators, and these machines are also available for individuals to keep them at home. The use of the automated external defibrillator has proven to be life-saving. Another option for individual use is a defibrillator vest.

It is a good idea for family members and friends of both VF survivors and patients with heart disease in general to take a CPR course. CPR courses are locally available through the American Red Cross, hospitals, or the American Heart Association.

Johns Hopkins patient information

Last revised: December 3, 2012
by Levon Ter-Markosyan, D.M.D.

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