Final answer:
Performing chest compressions is the next step in managing an unwitnessed cardiac arrest when there is no CPR in progress.
Step-by-step explanation:
In a situation where Adult Cardiac Arrest is unwitnessed by EMS and there is no CPR in progress, the next step in the management of the patient would be to perform chest compressions. Chest compressions help to circulate blood to vital organs and maintain minimal blood flow to the brain until advanced medical support arrives. Early initiation of chest compressions can improve the chances of survival.