A manual defibrillator, or defibrillator paddles, are used by physicians to deliver high intensity electrical charges to patients in ventricular fibrillation or cardiac arrest, restoring normal heart rhythm and restarting the flow of blood. Many popular television programs demonstrate emergency personnel loudly stating, “Clear!” before using the defibrillator paddles. This is done because anyone touching the person about to receive the shock may receive a shock himself or herself.

Manual defibrillators are also used in non-emergency situations in a procedure called elective cardioversion. In this procedure, lower levels of electricity are used to restore normal heart patterns in patients with non-emergency arrhythmias (e.g., atrial fibrillation). Cardioversion is the term doctors use to describe the delivery of a shock that is carefully timed to the waveform of the heartbeat, usually under controlled circumstances. This contrasts with defibrillation, which can occur at any point in the cardiac cycle and is usually performed under emergency circumstances.