What's the science behind "electric shock to save a life"?

"Electric shock" is known in medicine as electrical defibrillation, or electrical cardioversion. Medical devices that use electric shocks to rescue and treat arrhythmias are called defibrillators, also known as electrical cardioversion devices. A defibrillator produces a strong, controlled pulse of electrical energy that acts on the heart to eliminate certain heart rhythm disturbances and return it to sinus rhythm. This method of treating arrhythmias is called defibrillation or electrical cardioversion. The electrophysiologic basis, or scientific principle, for this emergency treatment technique is the presence of multiple foci of ectopic excitation in the heart during an acute infarction or other pathologic condition, or an inconsistency in the phase of activity of the various parts of the myocardium, which perpetuates the arrhythmia due to the refractory cycle of excitation. The purpose of the electric shock is to force the heart to be almost entirely depolarized in an instant, causing an instantaneous arrest, so that the phases of activity of the various parts of the myocardium are aligned. This makes it possible for the sinus node, which has the highest arrhythmia, to re-pace the heart, control the beat, and return to sinus rhythm. The short duration of electrical shock resuscitation is effective, with few side effects, in ventricular fibrillation, ventricular tachycardia, and atrial flutter and fibrillation. To date, electrical defibrillation is considered to be the most rapid and effective way to terminate ventricular fibrillation, the leading cause of cardiac arrest.