Compressing the chest helps to circulate blood (and the oxygen it contains) to the vital organs. Rescue breaths provide oxygen to the blood, a preliminary measure to provide oxygen before medical help arrives. While performing CPR, deliver cycles of 30 compressions around two rescue breaths.
The American Heart Association recommends that even untrained bystanders should begin CPR with chest compressions. Furthermore, untrained individuals should provide hands-only CPR. That means uninterrupted chest compressions of about 100 per minute until emergency personnel arrive. Those who are trained to perform CPR should begin with 30 chest compressions before checking the airway, after which 2 rescue breaths may be administered, along with additional cycles if necessary.