A defibrillator is a machine that uses a current of electricity to restart a heart that is beating erratically. Doctors and EMTs use a defibrillator when they perform CPR on a patient.
Defibrillator comes from defibrillation, literally "stopping fibrillation," or "stopping the heart from beating in an irregular way." The first defibrillators were demonstrated on dogs in 1899, but it wasn't until the 1950s that this method was used externally on humans, rather than during surgery. Even though movies often show doctors starting a stopped heart with a defibrillator, this isn't actually possible. What defibrillators do is closer to stopping an irregular heartbeat and shocking it into a normal rhythm.
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