Look for someone who can get an automated external defibrillator (AED) if available at the nearest emergency medical care center.
If there is no AED available, stay with the victim and call 911.

Lay the person on their back, and tilt their head back to lift their chin.
Remove any obvious blockages in the mouth or nose, such as vomit, blood, food, or loose teeth.

Listen carefully for breathing sounds for at least 10 seconds (except for occasional gasping sounds).
If you cannot hear breathing sounds, begin CPR.

Kneel next to the person's neck and shoulders.
Position both of your hands (lower palms) on top of each other in the middle of the person’s chest.
Compress (push straight down) the chest at least 2 inches (5 cm) but no more than 2.4 inches (6 cm).
Use your entire body weight (not just your arms) to deliver pressure at a rate of at least 100 compressions per minute.
Push hard and fast.
Allow a few seconds after each push so that the chest springs back.

Tilt the person's head back, lift their chin, pinch their nose shut, and place your mouth over their mouth to make a complete seal.
After mouth-to-mouth contact, blow to make the person’s chest rise.
If the chest rises, deliver a second breath.
Deliver at least two rescue breaths first, then continue compressions.

Continue with the chest compressions cycles and breathing until:
The person exhibits signs of life, such as breathing or movement.
An AED becomes available.
Emergency medical services or a trained medical responder arrives on the scene and takes over