Ventricular Fibrillation (V-fib)

Medically Reviewed by James Beckerman, MD, FACC on November 06, 2022
3 min read

Ventricular fibrillation, or V-fib, is a dangerous problem with your heart rhythm (called an arrhythmia) that keeps your heart from pumping blood the way it should. It is a medical emergency.

Your heart muscle has four main sections, called chambers. The bottom two chambers are the ventricles. Ventricular fibrillation happens when the electrical signals in your heart go haywire. This causes a ventricle to quiver (fibrillate) instead of pumping blood through your body.

Without medical treatment right away, V-fib can be deadly. In fact, it’s the most common cause of sudden cardiac death.

V-fib doesn’t give you much warning. The main symptom is fainting.

You may also have symptoms of ventricular tachycardia (VT). This is when the lower chambers of your heart beat too fast. It can lead to V-fib. Signs and symptoms of VT include:

  • Chest pain
  • Pounding or fast heartbeat
  • Dizziness
  • Nausea
  • Shortness of breath
  • Passing out

Sudden cardiac arrest is the worst thing that can happen with V-fib. The two main signs are not responding to someone touching or speaking to you, and having severe problems breathing (gasping for air or not breathing at all).

Doctors don’t know for sure what causes ventricular fibrillation. But they do know some situations have a link to it. For instance, it happens most often during or right after a heart attack. That may be because the heart’s electrical signals can become unstable when there isn’t enough blood flow.

Other things that can raise your chances of VFib include:

  • Weakened heart muscle (cardiomyopathy)
  • Prior heart attack
  • Certain genetic diseases
  • Certain heart medicines
  • Imbalance of electrolytes in the blood
  • Very low blood pressure (shock)
  • Electrical shock
  • Drowning
  • Problems with your main artery (aorta)
  • Drug toxicity
  • Severe infection (sepsis)


Your doctor will look at several things to learn whether you’re in V-fib. These may include:

  • Your symptoms
  • A physical exam
  • Your blood pressure, heart rate, and other vital signs

V-fib comes on quickly and needs treatment just as fast. If you get medical care right away, here’s what may happen:

  • Step 1: Cardiopulmonary resuscitation (CPR) to keep your blood moving
  • Step 2: Defibrillation to fix your heart rhythm
  • Step 3: Medication to make the rhythm stable again

Defibrillators for V-fib

You’ve probably seen defibrillators on TV, especially in medical dramas. They’re the paddles placed on a person’s chest to shock their heart into beating the way it should. This type is called an automated external defibrillator (AED). It can help save the life of someone who’s in cardiac arrest.

Two other types of defibrillators can also help someone with a dangerous arrhythmia such as V-fib.

  • Implantable cardioverter defibrillator (ICD). A surgeon places this device inside your chest or belly. When your heart is out of its regular rhythm, it gives high- or low-energy electrical shocks to get your heartbeat back to normal. (If your ventricles start to quiver, it will deliver a high-energy shock.) It’s like a pacemaker, but a pacemaker delivers only low-energy shocks.
  • Wearable cardioverter defibrillator (WCD). WCDs work much like ICDs, except they’re outside your body. Wires connect sensors on your skin to a unit you wear under your clothes. WCDs can be programmed to detect a certain type of arrhythmia, such as V-fib.

V-fib can lead to serious complications including:

  • Injuries from CPR
  • Skin burns from defibrillation
  • Brain injury from a lack of oxygen
  • Injury to your heart muscle
  • Death

You can’t completely prevent an episode of ventricular fibrillation. But there are a few ways to make it less likely:

  • Drugs that help control unusual heart rhythms (arrhythmia medications)
  • Devices that correct unusual heart rhythms (defibrillators)
  • Surgery to control unusual electrical signals (catheter ablation)