---
title: Ventricular fibrillation and sudden cardiac arrest
description: What ventricular fibrillation is, why it stops the circulation, what causes it, what a bystander should do, how resuscitation and a defibrillator help and how another cardiac arrest is prevented.
type: disease
preset: ventricular-fibrillation
aliases:
  - ventricular fibrillation
  - sudden cardiac arrest
  - VF
  - SCA
  - cardiac arrest
sources:
  - tier: guideline
    org: minzdrav-rf
    title: Желудочковые нарушения ритма сердца. Внезапная сердечная смерть
    year: 2025
    doi: 10.15829/1560-4071-2025-6670
    url: https://cr.minzdrav.gov.ru/view-cr/569_2
  - tier: guideline
    org: esc
    title: 2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death
    year: 2022
    doi: 10.1093/eurheartj/ehac262
    url: https://doi.org/10.1093/eurheartj/ehac262
  - tier: guideline
    org: nice
    title: Implantable cardioverter defibrillators and cardiac resynchronisation therapy for arrhythmias and heart failure (TA314)
    year: 2014
    url: https://www.nice.org.uk/guidance/ta314
  - tier: reference
    org: msd-manuals
    title: Ventricular Fibrillation (VF)
    year: 2024
    url: https://www.msdmanuals.com/professional/cardiovascular-disorders/specific-cardiac-arrhythmias/ventricular-fibrillation-vf
  - tier: reference
    org: msd-manuals
    title: Ventricular Fibrillation (Consumer Version)
    year: 2024
    url: https://www.msdmanuals.com/home/heart-and-blood-vessel-disorders/abnormal-heart-rhythms/ventricular-fibrillation
  - tier: reference
    org: msd-manuals
    title: Cardiac Arrest
    year: 2025
    url: https://www.msdmanuals.com/professional/critical-care-medicine/cardiac-arrest-and-cardiopulmonary-resuscitation-cpr/cardiac-arrest
  - tier: reference
    org: msd-manuals
    title: Cardiopulmonary Resuscitation (CPR) in Adults
    year: 2026
    url: https://www.msdmanuals.com/professional/critical-care-medicine/cardiac-arrest-and-cardiopulmonary-resuscitation-cpr/cardiopulmonary-resuscitation-cpr-in-adults
  - tier: reference
    org: msd-manuals
    title: Overview of Abnormal Heart Rhythms (Consumer Version)
    year: 2026
    url: https://www.msdmanuals.com/home/heart-and-blood-vessel-disorders/abnormal-heart-rhythms/overview-of-abnormal-heart-rhythms
sources_checked: 2026-10-13
review: null
---

Ventricular fibrillation (VF) is a rhythm disorder in which many chaotic electrical impulses keep the ventricles of the heart from contracting in a coordinated way: they only quiver.<Cite n={5} /> No blood is pumped out of the heart, so VF is a form of cardiac arrest, and without immediate treatment it causes death.<Cite n={5} /> Cardiac arrest stops blood from flowing to the organs and deprives them of oxygen.<Cite n={6} /> How the impulse normally travels through the heart is explained in the article on the [conduction system of the heart](../../anatomy/conduction-system/).

Sudden cardiac arrest is an unexpected stop of the circulation within an hour of the onset of acute symptoms that was reversed by resuscitation, for example by defibrillation.<Cite n={1} /> It often happens without warning.<Cite n={6} /> The definitions of sudden cardiac death and how VF is related to ventricular tachycardia are covered in the article on [ventricular tachycardia](../ventricular-tachycardia/).

<Diagram name="ventricular-fibrillation">
  <p slot="normal">
    Normally the impulse from the sinus node travels through the atria, passes the atrioventricular
    (AV) node down to the ventricles and spreads through them, making them contract.<Cite n={8} /> The
    walls of the chambers contract in a regulated sequence and pump blood.<Cite n={8} />
  </p>
  <p slot="disease">
    In VF, electrical impulses rapidly start firing from many sites in the ventricles at once, and the
    rhythm becomes uncoordinated.<Cite n={3} /> It is driven by many small re-entrant
    waves (multiple wavelets).<Cite n={4} /> The ventricles only quiver and do not contract in a coordinated way: no
    blood is pumped out of the heart.<Cite n={5} />
  </p>
</Diagram>

## Why it happens

<Patient>

The most common cause of VF is heart disease, above all too little blood flow to the heart muscle in [coronary heart disease](../coronary-heart-disease/), for example during a [heart attack](../myocardial-infarction/).<Cite n={5} /> Other causes are [heart failure](../heart-failure/), cardiomyopathies, shock, an electric shock, drowning, [long QT syndrome](../long-qt-syndrome/), some medicines that affect the electrical currents of the heart, and channelopathies, disorders of the heart's ion channels.<Cite n={5} />

Cardiac arrest is often the first sign of a heart disease the person did not know about.<Cite n={[1, 6]} /> The risk of VF is raised by abnormal levels of salts (electrolytes) in the blood, too much acid in the blood, too little oxygen in the blood and ischaemia.<Cite n={4} />

</Patient>

<Student>

The Russian Ministry of Health guideline defines VF as chaotic electrical activity in the form of polymorphic oscillations that constantly change in configuration, amplitude, duration and frequency, with a rate of 300 per minute or more.<Cite n={1} /> The mechanism is multiple wavelet re-entry.<Cite n={4} />

Most patients with VF have an underlying heart disorder: typically ischaemic cardiomyopathy, but also [hypertrophic](../hypertrophic-cardiomyopathy/) or [dilated](../dilated-cardiomyopathy/) cardiomyopathy or other arrhythmogenic disorders.<Cite n={4} /> According to the Russian guideline, coronary heart disease accounts for 75–80% of sudden cardiac deaths in Europe, while in the young primary electrical heart diseases, cardiomyopathies, [myocarditis](../myocarditis/) and coronary artery anomalies predominate.<Cite n={1} />

In [Brugada syndrome](../brugada-syndrome/) VF usually occurs at rest or during sleep; in [WPW syndrome](../wpw-syndrome/) the most dangerous manifestation is atrial fibrillation conducted over the accessory pathway, which can trigger VF.<Cite n={1} /> VF is much less common in infants and children than in adults: in them cardiac arrest more often presents as asystole.<Cite n={4} />

</Student>

<HeartModel highlight={['left-ventricle', 'right-ventricle']} />

## Symptoms

<Patient>

VF causes loss of consciousness within seconds.<Cite n={5} /> The person collapses without warning, sometimes with brief seizure-like jerks, then goes limp and does not respond.<Cite n={[5, 6]} /> They turn deathly pale, stop breathing and have no pulse.<Cite n={5} /> Oxygen no longer reaches the brain, and without help death follows within minutes.<Cite n={[4, 5]} />

A fast heartbeat (palpitations), feeling faint and fainting are the three most important symptoms that call for a visit to a doctor and further tests.<Cite n={1} /> More about them is in the article on [ventricular tachycardia](../ventricular-tachycardia/).

</Patient>

<Student>

Cardiac arrest is diagnosed clinically: unconsciousness, apnoea and pulselessness; arterial pressure is not measurable.<Cite n={6} /> On the ECG, VF appears as ultrarapid baseline undulations that are irregular in timing and morphology.<Cite n={4} />

</Student>

## How it is diagnosed

<Patient>

Cardiac arrest is recognised by its outward signs, and an [ECG](../../diagnostic/ecg/) shows that VF is the cause.<Cite n={5} />

In a person who has been resuscitated, doctors look for the cause of VF, above all coronary artery disease, cardiomyopathies and channelopathies.<Cite n={4} /> The ECG is recorded repeatedly and the rhythm is monitored, [echocardiography](../../diagnostic/echocardiography/) is done, and if the cause is unclear, imaging of the coronary arteries and cardiac MRI.<Cite n={[1, 2]} /> If the person already has a pacemaker, a defibrillator or a heart rhythm monitor, its recordings help show which rhythm disorder stopped the heart.<Cite n={1} />

If no cause is found after a full workup, the VF is called idiopathic.<Cite n={[1, 2]} /> Some of these people probably have an inherited disorder that has not been recognised, so family members are advised to be checked.<Cite n={5} /> Close relatives of someone who died suddenly are advised to see a cardiologist if the post-mortem found no clear cause.<Cite n={1} />

</Patient>

<Student>

ESC recommends that the investigation of a sudden cardiac arrest (SCA) survivor without an obvious extra-cardiac cause be overseen by a multidisciplinary team (I, B). In all survivors, repeated 12-lead ECGs during stable rhythm, including high precordial lead ECG, and continuous cardiac monitoring are recommended (I, B), as is echocardiography (I, C); without a clear underlying cause, coronary imaging and cardiac magnetic resonance (CMR) with late gadolinium enhancement (I, B). Collection of blood samples at presentation is recommended for potential toxicology and genetic testing (I, B).<Cite n={2} />

Idiopathic VF is diagnosed in an SCA survivor, preferably with documented VF, after exclusion of a structural, metabolic or toxicological aetiology and of channelopathies.<Cite n={[1, 2]} /> In about half of cases, relatives of sudden cardiac death victims are diagnosed with inherited arrhythmic diseases, above all channelopathies.<Cite n={1} />

</Student>

## How it is treated

<Patient>

Cardiac arrest from VF needs cardiopulmonary resuscitation (CPR) at once, and its key element is defibrillation, an electric shock that restores a normal rhythm.<Cite n={[1, 5]} /> The earlier the shock, the better the chance of restoring a normal rhythm.<Cite n={1} /> An automated external defibrillator (AED) lets someone with minimal training do this.<Cite n={7} /> That is why AEDs are recommended in places where many people gather, such as schools, airports, railway stations and stadiums.<Cite n={1} />

Once the circulation has been restored, the person is treated in a hospital with intensive care and the facilities for coronary artery procedures.<Cite n={1} />

People who survive VF are at high risk of another episode.<Cite n={5} /> If VF was caused by a reversible disorder, that disorder is treated.<Cite n={5} /> If there is no such cause, an implantable cardioverter defibrillator (ICD) is recommended.<Cite n={[1, 2, 3]} /> This is a small battery-powered device placed under the skin just below the collarbone, with thin wires (leads) in the heart.<Cite n={3} /> It constantly monitors the rhythm, detects VF by itself and delivers a shock.<Cite n={5} /> Living with an ICD is covered in the article on [ventricular tachycardia](../ventricular-tachycardia/).

Medicines for arrhythmia are often given as well to make episodes less frequent, but they do not stop an arrhythmia once it has started.<Cite n={[3, 4, 5]} /> To lower the risk of sudden death, the underlying heart disease is treated and risk factors are reduced.<Cite n={1} /> The doctor decides which treatment is needed.

</Patient>

<Student>

In sudden cardiac arrest (pulseless VT or VF), immediate CPR is clearly recommended, with emergency defibrillation as its key element.<Cite n={1} /> ESC recommends prompt CPR by bystanders in out-of-hospital cardiac arrest, public access defibrillation at sites where cardiac arrest is more likely to occur, and community training in basic life support (all I, B).<Cite n={2} /> The MSD Manual describes chest compressions in adults at a rate of 100 to 120 per minute and a depth of 5 to 6 cm; for a lay rescuer who is unwilling or unable to give mouth-to-mouth rescue breaths, compression-only CPR is recommended.<Cite n={7} /> Compressions are resumed immediately after the shock.<Cite n={7} />

An ICD is recommended in documented VF or haemodynamically not tolerated VT in the absence of reversible causes (ESC: I, A), and in idiopathic VF (I, B).<Cite n={2} /> The Russian guideline recommends it in the absence of transient causes and more than 48 hours after the onset of myocardial infarction.<Cite n={1} /> Apart from beta-blockers, no antiarrhythmic drug has been shown to reduce all-cause mortality.<Cite n={1} />

</Student>

## When to call an ambulance

**Someone suddenly collapses, does not respond and is not breathing or is only gasping**: this may be cardiac arrest.<Cite n={[6, 7]} />

- Shout for help and call your local emergency number at once (112 in the EU, 911 in the US and Canada, 999 in the UK).<Cite n={[1, 7]} /> If someone else is there, let them make the call and, if possible, fetch a defibrillator.<Cite n={7} />
- Start CPR at once: even an untrained person should begin continuous chest compressions and keep going until help arrives.<Cite n={[1, 2, 7]} /> In many emergency services the dispatcher talks callers through chest compressions over the phone.<Cite n={7} />
- As soon as an automated external defibrillator arrives, use it.<Cite n={[1, 7]} />

The earlier resuscitation and defibrillation start, the better the chances: early bystander CPR, a witnessed arrest and early defibrillation all favour survival.<Cite n={6} /> The Russian guideline suggests considering basic resuscitation training for relatives of people at high risk of sudden death too.<Cite n={1} />

<Quiz />