Answer:
Begin CPR.
Step-by-step explanation:
For an unwitnessed cardiac arrest, assuming you have already conducted a scene size up and ensured your own personal safety and there is no breathing or no pulse you should begin CPR. It's important to provide high quality chest compressions and rescue breathing at the proper rate dependent on the victim's age and the number of rescuers since the ratio can change due to these factors.
Single Rescuer Adult: 30:2
Two Rescuer Adult: 30:2
Single Rescuer Child/Infant: 30:2
Two Rescuer Child/Infant: 15:2