The primary purpose of defibrillation is to deliver an electric shock to the heart with the aim of stopping abnormal heart rhythms and restoring a normal heartbeat. This process is essential during certain life-threatening arrhythmias, such as ventricular fibrillation or pulseless ventricular tachycardia, where the heart is quivering rather than effectively pumping blood. The electric shock helps to depolarize the heart muscle cells all at once, allowing the normal pacemaker cells to regain control, thereby establishing a more coordinated and effective rhythm.
Considering the other options, restarting the heart after cardiac arrest is not exclusively accurate for defibrillation; it is rather a more nuanced outcome of restoring normal rhythm. Increasing heart rate during bradycardia is managed through different interventions and not through defibrillation, as that procedure focuses on correcting severe arrhythmias rather than simply elevating the heart rate. Similarly, stimulating heart muscle contractions typically refers to pacing, not defibrillation, which is specifically aimed at resetting the heart's electrical activity rather than stimulating contractions directly.