What is the primary reason for using an Automated External Defibrillator (AED)?

Using an Automated External Defibrillator (AED) primarily serves the critical purpose of restarting the heart after a cardiac arrest. When someone experiences a cardiac arrest, the heart is unable to pump blood effectively due to irregular heart rhythms, often leading to a loss of consciousness and cessation of breathing. An AED is designed to analyze the heart's rhythm and, if necessary, deliver an electric shock to restore a normal rhythm. This process can be crucial in increasing the chances of survival and can significantly improve the outcomes for the individual experiencing cardiac arrest.

The other options, while important in different medical contexts, do not accurately represent the primary function of an AED. Monitoring heart rate is a function of other medical devices but is not the AED's role. Similarly, administering medication is not something an AED does, nor is providing oxygen, which typically involves separate equipment such as oxygen tanks or bag-mask devices. The AED's specific role in defibrillation is what makes it an essential tool in emergency situations involving cardiac arrest.