Final answer:
In a cardiac emergency where an adult is unresponsive and not breathing, you should check for breathing, call EMS (911), begin chest compressions immediately, and use an AED as soon as possible.
Step-by-step explanation:
When you encounter an unresponsive adult and you are trained in CPR, the first action is to ensure the scene is safe, then tap the person and shout. If there is no response, you need to check if the person is breathing. If they are not breathing or only gasping, call for help immediately. One person should call EMS (911) and retrieve an AED if available, while another begins chest compressions. The correct sequence in a cardiac emergency is to assess the person, call for help, begin chest compressions to circulate blood, and use an AED as soon as it becomes available.
If only one rescuer is present, they should start chest compressions immediately and then seek help as quickly as possible. Chest compressions are performed by placing the flat portion of one hand on the center of the person's chest, between the nipples, and pressing down hard and fast at least 5 cm deep and at a rate of 100 compressions per minute.
Remember, CPR and the use of an AED can significantly increase the chances of survival for someone experiencing cardiac arrest. It's crucial to act swiftly and confidently, calling for a bystander to help if available.