Which device is used to restore a normal rhythm to the heart when a patient is in cardiac arrest and presents with a rapid, weak heartbeat?

The Automated External Defibrillator (AED) is designed specifically for emergencies involving cardiac arrest, especially when a patient exhibits a rapid and weak heartbeat, also known as arrhythmia. The AED is a portable device that analyzes the heart's rhythm and, if necessary, delivers an electric shock to restore a normal cardiac rhythm. This capability is crucial in life-threatening situations, as timely defibrillation can greatly increase the chances of survival.

While manual resuscitators and CPR machines are valuable for providing respiratory support and maintaining blood circulation through chest compressions during cardiac events, they do not directly address the issue of an abnormal heart rhythm that an AED targets. A pulse oximeter measures the saturation of oxygen in the blood and can indicate respiratory efficiency but does not have a role in restoring heart rhythm. Thus, the AED is the appropriate and effective choice in this scenario for restoring a normal rhythm to the heart.