What Is Ventricular Fibrillation?

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Ventricular fibrillation, the No. 1 cause of sudden cardiac arrest, impacts the flow of blood to the body and may result in severe consequences to one’s health. 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 that control the pumping of blood.

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 abnormal heart rhythm (called an arrhythmia) 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 further cause blood pressure to fall, resulting 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.

Treatment includes cardiopulmonary resuscitation (CPR) and delivered shocks to the heart via an automated external defibrillator (AED), often found 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 prevent sudden cardiac death.


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

Untreated and prolonged ventricular tachycardia may eventually evolve into ventricular fibrillation, with symptoms arising prior to onset.

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). Observing QRS complexes, which are the graphical reflections of the ECG, can indicate the loss of regular, normal heart rhythm or failing electrical conduction of the heart and its inability to pump blood.


There are a variety of causes of ventricular fibrillation. Having experienced a prior heart attack, leading to scar tissue and damage to the electrical system of the heart, is the most common cause of this condition. Ventricular fibrillation can occur in people with no history of heart disease, yet heart disease risk factors such as smoking, diabetes, and high blood pressure can increase the risk.

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
  • 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

A variety of health conditions can also lead to ventricular tachycardia. Some of these include:

  • Congenital (present at birth) heart disease
  • A history of heart attack
  • Heart muscle disease (cardiomyopathy) that causes weakened, stretched, or thickened heart muscle
  • Prolonged, untreated ventricular tachycardia
  • Issues with 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 express symptoms and then suddenly collapse, giving no time to fully diagnose the individual. 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 unresponsive. If unresponsive, 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 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. 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.

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.

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.


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, a person experiencing ventricular fibrillation can experience death. During an episode, there is a great 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 symptoms that precede 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 implanted near your left collarbone, with one or more flexible and insulated wires running from the ICD through veins to your heart. These devices can be implanted to monitor and correct abnormal heart rhythms.

If a slow heart rhythm is detected, an electrical signal is sent to speed up and pace (like a pacemaker) your heart. If the heart rhythm is too fast (such as in ventricular tachycardia), or you are experiencing ventricular fibrillation, a low- or high-energy shock will be sent from the ICD in order to reset your 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 the medical condition stabilizes after an episode of ventricular fibrillation.

Coronary Angioplasty and Stent Placement

While this procedure is typically used for the treatment of severe coronary artery disease, if ventricular fibrillation occurs due to a heart attack, a cardiologist may recommend this procedure in order to reduce the risk of future episodes. Coronary angioplasty and stent placement opens blocked coronary arteries, allowing blood to flow more efficiently to the heart.

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 your 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 the coronary angioplasty and stent placement, coronary bypass surgery is also 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, and may reduce the risk of ventricular fibrillation.

A Word From Verywell

Issues with cardiac health can be daunting. 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 changes to diet, like increasing consumption of vegetables and fruit and fish, and reducing red meat, can help reduce these risk factors.

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. In this training, you will learn the proper method of delivering compression and breaths and how to use an AED.

If you are experiencing ventricular tachycardia, or have experienced ventricular fibrillation, make sure to have routine follow-ups with a primary care provider, a cardiologist, and, as needed, immediate emergency evaluations.

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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.
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  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.

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