When a person collapses in cardiac arrest, they need CPR. For a person who is unresponsive and not breathing, immediately call 9-1-1 and put the phone on speaker mode so you can talk to the dispatcher while beginning CPR.
Begin pushing hard and fast in the center of the chest. Compress the chest two inches at the rate of 100-120 per minute until help arrives.
If an AED becomes available, use the AED as soon as it arrives. AEDs are incredibly simple to operate. An AED might turn on automatically, or may have an "on" button. After the AED is turned on, the machine will instruct you how to use it.
For more information, visit the American Heart Association website: