Final answer:
In a cardiac emergency, the next step would be to use the automated external defibrillator (AED) on the unconscious infant. Before using the AED, it is recommended to perform CPR on the infant.
Step-by-step explanation:
In a cardiac emergency, the next step would be to use the automated external defibrillator (AED) on the unconscious infant. AEDs are designed to be used by lay persons and are commonly found in many public places as well as ambulances. The device automatically diagnoses the patient's heart condition and applies the shock with appropriate energy and waveform.
Before using the AED, it is recommended to perform CPR (cardiopulmonary resuscitation) on the infant. CPR helps maintain blood flow and oxygen to the body until the AED can be used. If performed correctly and promptly, CPR can increase the chances of survival.