Ventricular Fibrillation vs Cardiac Arrest

What's the Difference Between Ventricular Fibrillation and Cardiac Arrest?

ekg monitor defibrillator
Cardiac defibrillator on a stretcher. Keith Brofsky / Getty Images

Ventricular fibrillation causes cardiac arrest, but not all cardiac arrest is caused by ventricular fibrillation.

Cardiac arrest is the term that describes when a heart stops pumping blood around. When a victim's heart stops pumping blood and he or she stops breathing (which usually happens within a few seconds of the heart stopping), the victim is considered clinically dead. If the victim's heart doesn't start again or CPR isn't started within 4 minutes of cardiac arrest, brain damage is almost guaranteed.

Ventricular fibrillation is a form of heart rhythm disturbance (dysrhythmia) that causes cardiac arrest. During ventricular fibrillation, the heart stops beating normally and simply begins quivering uncontrollably. No blood is pushed through because there is no squeezing action.

Believe it or not, if you have to go into cardiac arrest, ventricular fibrillation is the best case scenario. Ventricular fibrillation responds very well to electric shock, which stops the quivering and lets the heart's normal electrical activity start over. That's why we call those shock boxes defibrillators.

Other Lethal Dysrhythmias

Ventricular fibrillation (v-fib) is not the only dysrhythmia that causes cardiac arrest. There are several. Not all of them respond to electricity as favorably as v-fib.

The second best option is called ventricular tachycardia (v-tach) and is treated exactly the same as v-fib. The difference is that ventricular tachycardia continues to make the heart beat regularly, but it goes so fast that the heart never gets a chance to fill with blood.

There's not an opportunity to build up the pressure, so the blood stops flowing.

Asystole is the term for a lack of any sort of heart beat at all. On an EKG machine, asystole is a simple, flat line. Asystole is the worst case scenario because it means there is absolutely no electrical activity in the heart for rescuers to work with.

At least with v-fib or v-tach, the heart can be shocked, which stops it from moving for a second and gives it a chance to start over. Think of defibrillation as a reboot for your heart. It doesn't always work, but when it does, it's pretty amazing.

Agonal rhythm is a term for the last attempts of the heart to try beating. It's treated no differently than asystole (rescuers attempt to wake the heart up using a combination of CPR and drugs known to make the heart irritable again). However, agonal rhythm is slightly better only because we know the heart has at least a little energy left in it.


Herlitz, J., et al. "Characteristics of Cardiac Arrest and Resuscitation By Age Group: an Analysis From the Swedish Cardiac Arrest Registry." American Journal of Emergency Medicine. Nov 2005

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