Science
How does a defibrillator work?
A defibrillator works by delivering a controlled electric shock to a heart that is quivering chaotically, briefly stopping all its electrical activity. This lets the heart's natural pacemaker restart a normal, coordinated rhythm.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how a defibrillator works.
Step by step
- 1A dangerous rhythm (fibrillation) makes the heart quiver instead of pump.
- 2The device sends a strong, brief current across the heart.
- 3The shock resets all heart cells at once, halting the chaos.
- 4The heart's own pacemaker can then resume a normal beat.
- 5Automated external defibrillators (AEDs) guide bystanders by voice.
Frequently asked questions
- Does a defibrillator restart a stopped heart?
- Not exactly — it stops a chaotic rhythm so the heart's natural pacemaker can take over. It can't jump-start a heart with no electrical activity at all.
- What is an AED?
- An automated external defibrillator — a portable device that analyzes the heart's rhythm and talks a bystander through delivering a shock if needed.
- Can anyone use a defibrillator?
- Public AEDs are designed for untrained bystanders, giving spoken steps and only shocking when the rhythm calls for it.