Defibrillator

Defibrillators apply brief high-voltage electric to the heart, to restore a proper rhythm. The shock may be under the control of a individual qualified to interpret the electrical activity of the heart, or by a computer programmed to recognize and react to specific arrythmias. Such a computer may be external or internal to the body. Manual defibrillators most commonly are

They are lifesaving when the heart goes into purposeless ventricular fibrillation (VF) or ventricular tachycardia (VT), conditions that do not move enough blood to create a pulse. Essentially, they stop and restart the heart, with the its muscles contracting in the proper rhythm.

External cardioverter

Some defibrillators may have a mode in which they synchronize to a point on the patient's electrocardiogram waveform, and apply a lower-power shock than used for VF or VT. These restore the proper rate and shape of the heart rhythm in arrythmia]s such as atrial fibrillation (AF).