Final answer:
Electrical shock delivered by a defibrillator is primarily used to treat life-threatening heart arrhythmias like ventricular fibrillation, wherein it 'resets' the heart's rhythm.
Step-by-step explanation:
Application of electrical shock to the heart is usually used to treat heart arrhythmias, particularly ventricular fibrillation, a condition where the heart beats in a fast, irregular manner preventing effective blood pumping. In this emergency, a device called a defibrillator can apply a controlled electric shock, effectively stopping the heart momentarily and allowing the heart's natural pacemaker to reset to a normal rhythm. Automated external defibrillators (AEDs) are now commonly found in public places and are designed for use by laypersons, providing verbal instructions and automatically diagnosing the heart condition before applying a shock with the appropriate energy and waveform.