What Is Ventricular Fibrillation?

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Ventricular fibrillation, the No. 1 cause of sudden cardiac arrest, impacts the flow of blood in the body and may result in severe health consequences. Within seconds, a person experiencing ventricular fibrillation can have no sign of a pulse and become unresponsive. Prompt administration of cardiopulmonary resuscitation (CPR) and the use of a defibrillator can preserve oxygen delivery and significantly reduce the risk of death.

Woman learning how to do CPR

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What Is Ventricular Fibrillation?

Ventricular fibrillation is a condition that is characterized by rapid, erratic heartbeats that cause the heart to abruptly stop effectively pumping blood to the body. This occurs due to disordered electrical impulses in the heart.

When ventricular fibrillation occurs, pumping chambers in the heart, called ventricles, twitch or quiver and are unable to contract normally and pump blood. Ventricular fibrillation is reported as the most frequent cause of sudden cardiac death.

This form of arrhythmia (abnormal heart rhythm) is life-threatening and is considered a medical emergency that requires immediate attention and emergency treatment.

In the U.S., about 300,000 people die suddenly from ventricular fibrillation annually. Ventricular fibrillation is sometimes triggered by a heart attack and can cause blood pressure to suddenly fall. This results in a shortage of blood supply and oxygen to vital organs, including the brain. Within seconds, a person can collapse and go into cardiac arrest.

Urgent treatment includes CPR and shocks to the heart via an automated external defibrillator (AED). These devices are often placed in heavily trafficked public places and medical settings.

For those at risk of ventricular fibrillation, medications and implantable devices that restore a normal heart rhythm can be used to regulate the heart rhythm and prevent sudden cardiac death.


Ventricular fibrillation often starts as ventricular tachycardia, which are rapid heartbeats caused by abnormal electrical impulses originating in the ventricles. With nonsustained ventricular tachycardia, the rhythm abnormality lasts less than 30 seconds, and symptoms may not arise.

Untreated and prolonged ventricular tachycardia may eventually cause symptoms and can evolve into ventricular fibrillation.

Symptoms of prolonged ventricular tachycardia include:

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

Signs of ventricular fibrillation can also be detected by an electrocardiogram (known by the acronyms of ECG or EKG). Certain pattern alterations in the EKG waves described as QRS complexes can indicate the loss of regular, normal heart rhythm.


There are a variety of causes of ventricular fibrillation. A heart attack is a common cause. A heart attack can lead to scar tissue and damage to the electrical system of the heart.

Heart disease risk factors such as smoking, diabetes, and high blood pressure can increase the risk, but people who don't have these risk factors can also develop ventricular fibrillation.

Causes of ventricular fibrillation include:

  • Injury to the heart, including electrocution accidents, or physical trauma to the area directly over the heart, resulting in sudden cardiac death (commotio cordis)
  • Angina or chest pain due to reduced blood flow to the heart muscle
  • A history of heart surgery
  • Certain medications
  • The use of illegal drugs, like cocaine or methamphetamine
  • Significant electrolyte abnormalities, such as abnormal potassium or magnesium levels

Certain health conditions can lead to ventricular tachycardia.

Some of these include:

  • Congenital (present at birth) heart disease
  • A history of heart attack
  • Heart muscle disease (cardiomyopathy) can cause weakened, stretched, or thickened heart muscles
  • Prolonged, untreated ventricular tachycardia
  • Structural problems of the aorta, the largest artery leaving the heart
  • Very high or very low potassium levels in the blood
  • Sepsis (severe body infection)


Within seconds, a person experiencing ventricular fibrillation can develop symptoms and then suddenly collapse, giving no time for a medical evaluation. If you or someone else is experiencing symptoms, it is important to seek emergency medical help immediately.

If Someone Is Experiencing Ventricular Fibrillation

The following are critical steps to take if you are witnessing a situation where a person may be experiencing ventricular fibrillation or sudden cardiac arrest:

  1. Call 911 or the emergency number in your area.
  2. Check to see if the person is responsive or unresponsive and check for a pulse.
  3. If there is no pulse, immediately begin cardiopulmonary resuscitation (CPR) to maintain as much blood flow to the organs as possible until a portable automated external defibrillator (AED) can be applied and used to deliver an electrical shock (defibrillation) to the heart.

During CPR

Make sure to push hard and fast on the person’s chest, right above their sternum, delivering about 100 compressions per minute.

  • If they have a pulse and you have been trained in CPR, you may also check the person’s airway to ensure it is clear of any obstructions and deliver several rescue breaths, fully inflating their lungs.
  • If they don't have a pulse or you haven't been trained in CPR, do not give rescue breaths or check the airway—CPR should be started immediately with a 30:2 ratio of compressions to breaths.

The most crucial component in this situation is giving the chest compressions until help arrives.

When a Portable AED Is Available

Simply turn on the device and follow the built-in, voice-guided instructions. This device is programmed to deliver a shock that could help restart heartbeats, but only when needed. The shock will momentarily reset the heart and the chaotic rhythm, allowing the normal heart rhythm to resume.

Portable AEDs are becoming more and more available in a variety of places, including airplanes, cruise ships, shopping malls, and can even be purchased for your home.

Make certain you and other bystanders are physically clear of the device, the down person, and any pooled water prior to the delivery of the shock or you may become electrocuted.


Treatments for ventricular fibrillation include immediate emergency treatment and long-term treatment to restore the regular heartbeat.

An unresponsive person with no pulse should be treated immediately, as they may be experiencing ventricular fibrillation, and would require the restoration of a normal heart rhythm to survive. If you encounter someone experiencing these symptoms, immediately call for help and begin delivering CPR. If an AED is available, turn on the device and follow the instructions as you use it.

Within minutes, ventricular fibrillation can cause death. During an episode, there is a potential risk of damage to the brain and other vital organs. While in some cases, episodes of ventricular fibrillation may be stabilized, this condition is the most frequent cause of sudden cardiac death. 

For those experiencing non-emergency symptoms of ventricular fibrillation, or are in a stabilized condition after an episode, there are a variety of long-term treatments that might reduce the risk of future episodes of ventricular fibrillation or cardiac arrest.


Arrhythmia medications may be prescribed to help control general disturbances in heart rhythms. Anti-arrhythmic drugs may be used for emergency or long-term treatment of ventricular fibrillation. Those at risk of ventricular fibrillation or sudden cardiac arrest are commonly prescribed drugs called beta-blockers.

Implantable Cardioverter Defibrillator (ICD)

ICDs are battery-powered units that are surgically implanted near the left collarbone, with one or more flexible and insulated wires running from the ICD through veins to the heart. These devices can be implanted to monitor and correct abnormal heart rhythms.

If the ICD detects a slow heart rhythm, an electrical signal is sent to speed up and pace the heart, like a pacemaker. If the heart rhythm is too fast (such as in ventricular tachycardia), or if ventricular fibrillation is detected, a low- or high-energy shock will be sent from the ICD to reset the heart to a normal rhythm.

These devices are more effective than medications for arrhythmia-induced cardiac arrest prevention, and a cardiologist might recommend the implantation of an ICD after an episode of ventricular fibrillation stabilizes.

Coronary Angioplasty and Stent Placement

If ventricular fibrillation occurs due to a heart attack, a cardiologist may recommend this procedure to reduce the risk of another heart attack. Coronary angioplasty and stent placement opens blocked coronary arteries, allowing blood to flow more efficiently to the heart muscles.

During the procedure, the doctor will insert a long, thin tube (catheter) and pass it through a smaller artery, in either the leg or the arm, and to a blocked artery in the heart. This catheter is made with a unique balloon tip that inflates for a brief period, opening up the blocked coronary artery.

If stent placement is also recommended, the doctor will insert the metal mesh stent into the artery to keep it open long term. This restores blood flow to the heart.

Coronary Bypass Surgery

Like coronary angioplasty and stent placement, coronary bypass surgery is conducted to improve blood flow.

During the procedure, the cardiovascular surgeon will sew the veins or arteries in places at a point beyond the blocked or narrowed coronary artery, bypassing the obstruction. This will restore blood flow to the heart to prevent a heart attack, which may reduce the risk of ventricular fibrillation.

A Word From Verywell

Issues with cardiac health can be scary. If you or someone you know is interested in improving long-term cardiac health, start with reducing risk factors, such as diabetes, hypertension (high blood pressure), and hyperlipidemia (excessive fats in the blood). Regular aerobic exercise and healthy dietary habits, like incorporating vegetables and fruit and fish, and reducing red meat, can help reduce these risk factors.

If you have ventricular tachycardia or ventricular fibrillation, make sure to have routine follow-ups with a primary care provider and a cardiologist.

Getting CPR training can help you learn the basics on how to respond during a situation where someone around you may be experiencing ventricular fibrillation, which may possibly help to save their life. During this training, you will learn the proper method of delivering compression and breaths and how to use an AED.

8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Ludhwani D, et al. Ventricular fibrillation. StatPearls Publishing.

  2. Srinivasan, NT, et al. Sudden cardiac death and arrhythmias. Arrhythm Electrophysiol Rev. 2018 Jun;7(2):111–117. doi:10.15420/aer.2018:15:2

  3. American Heart Association. Ventricular fibrillation.

  4. MedlinePlus. Ventricular fibrillation.

  5. National Heart, Lung and Blood Institute. Defibrillators.

  6. American Heart Association. Implantable cardioverter defibrillator.

  7. MedlinePlus. Angioplasty and stent placement.

  8. MedlinePlus. Coronary artery bypass surgery.

Additional Reading

By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.