Ventricular Fibrillation

Ventricular Fibrillation

Ventricular Fibrillation

Ventricular fibrillation or VF occurs when there are uncoordinated contractions within the ventricles of the heart. The primary cause of VF is hypoxia (lack of oxygen) to the heart muscle which causes hyperirritability in the cardiac muscle tissue.

As a result, multiple muscles cells within the ventricles simultaneously fire as pacemakers causing a quivering or fibrillation that is ineffective for adequate cardiac output.

Ventricular Fibrillation ECG Tracing

The two images above show what ventricular fibrillation will look like on a EKG rhythm strip.

VF can rapidly lead to heart muscle ischemia and there is a high likelihood that it will deteriorate into asystole.

Ventricular fibrillation is treated using the left branch of the pulseless arrest arrest algorithm. Click below to view the pulseless arrest algorithm diagram. When done click again to close the diagram.
Pulseless Arrest Algorithm Diagram.

Ventricular fibrillation is always pulseless and must be confirmed by EKG or defibrillator monitor. Defibrillation is the treatment of choice and should occur as soon as possible.

The video below shows an example of what ventricular fibrillation will look like when you see it on the defibrillator monitor. Please allow several seconds for the video to load.


  1. says

    This is a very useful site.Thanks for all your help.Just wanted to ask We have an AED instead of a DEFIBRILLATOR.Can I use AED instead of a Defibrillator for shock in PULSELESS VT/VF.

  2. Nancy says

    I love your site. one question on exam was “What would be your very first action if you have pulseless V.T.
    The answer was defib. first and yet the algorithm says to start C.P.R. first.
    Thank you Nancy

    • says

      If the patient is attached to the defibrillator then the first action would be defibrillation. If the defibrillator is not attached then you would start CPR. Was this not made clear in the question?
      Kind regards,

  3. patrickfanelli says

    I have the AHA provider manual and it puts me to sleep! I have just started using you website for 10 min and I am already hooked! This will probably be the best 16.95 I ever spent! I am a Wildland Fire Fighter in FL. So I do not run any medical calls. But I am also a Paramedic and this site is going to keep my skills up to date and prepare me for my renewal . Good job with this site!


  4. says

    THANK YOU to whoever set this website up and keep it running smoothly!!! It is so awesome, so easy to learn, and entertaining as well: love the drama music during rhythm videos. May God bless you and give you many donations for your efforts!

  5. Marcella says

    Just started! This is awesome! I’ve passed courses in the past, but this time I’m understanding. Thank you!

  6. runtherace10 says

    Just signed up and having a great time studying this. I’m motivated every time I login to learn more! Question about the left branch of the pulseless arrest algorithm. After you get down to the bottom of the flow chart (CPR 2 minutes/5 cycles) and give Amiodarone and treat reversible causes, the arrow goes back up to the top of the first box in the flowchart. I’m assuming that you continue with CPR 2 minutes/5 cycles (obviously IV/IO access has already been obtained so no need to repeat this again). But if the rhythm is shockable and you administer the shock, do you give a second round of Epinephrine every 3-5 minutes again and if you need to perform another shock do you give another round of Amiodarone again (and so on if you have to keep repeating the loop)? Thanks!

    • says

      The medications are basically on their own timeline. Amiodarone is usually only given twice 300mg and then 150mg. After this, the patient has been so long in cardiac arrest there is little likelihood that ROSC will be achieved.
      Regarding epinephrine, the first dose is given after the second shock during CPR and then it is on it’s on time schedule and given every 3-5 minutes. The physical actions of CPR-Rhythm check-Shock are basically what you are doing for the repeating loop. Hope this makes sense.

      Kind regards,

      • IS says

        Hi, I wanted to clarify something: you mention that EPI is given after the 2nd shock. If that is the case, when is the first shock administered? Immediately once the defib pads are attached?
        SOrry, if it’s a dumb questions, but just getting reacquainted with the subject- it’s been awhile!

      • says

        It depends on if the cardiac arrest was witness or unwitnessed. If the cardiac arrest was witnessed then you immediately shock the pt. If the cardiac arrest was unwitnessed, you will provide 5 cycles of CPR and then shock.

        Kind regards,

  7. says

    today i had one 61 oldman with acute anterolateral MI. his intial bp-76/42. i gave fluid challnge- bp improved to 116/80. given asprin 300mg + clopidogrel 300mg. gtn withheld due hypotension. during observation he developed vf. i gave intial shock-200joules (biphasic). reverted to sinus rhythm. after 5monites he developed vt followed by vf. second shock of 360 joules given. is it correct to give intial 200j then 360 joules?

    • says

      You could have given 300 J for the second dose but many MD’s just go straight to 360 J. What you did was appropriate. AHA ACLS guidelines say “200 then 300 then 360,” but these are just recommendations. What you did was OK. A heparin drip should also have been started and he should have received coronary intervention asap.

      Kind regards,

      • says

        It is ok to give a shock to a patient that is conscious. It is not preferred, but in an emergency, it can be done. I have seen this done several times.
        Also, there are some people who have internal defibrillators that shock them when there heart goes into VT.
        It is definitely not a pleasant feeling and light sedation is preferred.

        Kind regards,

    • says

      VF and Pulseless VT are treated using the left branch of the pulseless arrest algorithm. Both VF and pulseless VT respond quite well to defibrillation and the left branch of the pulseless arrest algorithm has proven to be the most effective method of treatment for VF.

      Kind regards,

      • slayer says

        Well why call it “pulseless VF?” Is there such a thing as VF with a pulse?!? When you put “pulseless” in front of VF/VT it confuses students new to ACLS. When new students try to figure this out for the first time seeing “pulsless” then advising a shock is confusing, since Pulseless Electrical Activity dosnt require a shock. Its ok to remind people that VF/VT patients wont have a pulse, but putting “pulseless” in the title will lead to unnecessary confusion between VT/VF and PEA. (I know a little studying will clear this up but I can see how confusing and frustrating this can be for first timers.)

      • says

        I’m not sure where you saw pulseless VF. VF is always pulseless. In several places I have written Pulseless VT/VF and this means pulseless VF and VF.
        You will use defibrillation on pulseless VT. You will not use defibrillation on VT. VT may have a pulse and in the case that it does, you will use synchronized cardioversion. You have to clarify on whether you are dealing with pulseless VT or VT.
        I like to explain it by stating that Pulseless VT and VF are the two exception to the rule when it comes to PEA. This is why there are two branches to the pulseless arrest algorithm. The left branch for Pulseless VT/VF and the right branch for PEA/Asystole.
        Thanks for helping to clarify.

        Kind regards,

  8. KIM says

    this site is really helpful..:) i just wanted to ask something.. is it safe to deliver a shock when the patient is hooked with oxygen?

  9. Blonde4fun says

    By far the best ACLS tutorials! Lots of great tips on how to distinguish rhythms (especially the heart blocks) and explanations that are simple and easy to remember. Thank you for all the time and energy you put into your work. It makes my job of passing ACLS easier.

  10. Celeste Hovagimian says

    I’m new at this. How can you distinguish between pulseless ventricular tachycardia and ventricular fibrillation on an ECG strip?

    • says

      Ventricular fibrillation will be very disorganized and will not have a pattern. Also, you will not be able to determine the heart rate because the rhythm is disorganized.

      Ventricular tachycardia will have a very rapid rate which usually greater than 180/min. The rhythm will appear organized and you should be able to count the beats, but the rate will be extremely high.

      I would encourage you to review the above page and also the link below:

      Kind regards,

  11. aclsnursewh says

    I am a new grad and my first ACLS course is coming up very soon!! I want to pass! So far I love the videos and information available. Thank you

  12. Thomas A. Lucas, M.D. says

    My goodness! This is shocking! Please keep up this beautiful, well constructed helpsite. Out here in the boonies we need the help. THANKS!

    • siobhansiobhan says

      lol shocking har har :) i’m enjoying learning with the discussions underneath, and i’m enjoying this too. resident in fam med doing emerg

  13. poonam says

    This is site is definitely very helpful and i hope that it remains helpful in future. I love this site, thank you so much.

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