Check the scene for immediate danger.

Make sure you're not putting yourself in harm's way by administering CPR to someone unconscious. Is there a fire? Is the person lying on a roadway? Do whatever is necessary to move yourself and the other person to safety.

Assess the victim's consciousness.

Gently tap his or her shoulder and ask "Are you OK?" in a loud, clear voice. If he or she responds, CPR is not required.

Send for help.

The more people available for this step, the better. However, it can be done alone. Send someone to call for emergency medical services (EMS).

Give the dispatcher your location, and notify him or her that you're going to perform CPR. If you're alone, get off the phone and start compressions after that. If you have someone else with you, have him or her stay on the line while you do CPR on the victim.

Do not check for a pulse.

Unless you're a trained medical professional, odds are you'll spend too much valuable time looking for a pulse when you should be doing compressions.

Check for breathing.

Put your ear close to the victim's nose and mouth, and listen for slight breathing. If the victim is coughing or breathing normally, do not perform CPR. Doing so could cause the heart to stop beating.

Place the victim on his or her back.

Make sure he or she is lying as flat as possible - this will prevent injury while you're doing chest compressions.

Place the heel of one hand on the victim's breastbone, exactly between the nipples.

Place your second hand on top of the first hand, palm-down.

Position your body directly over your hands, so that your arms are straight and somewhat rigid.

Perform 30 chest compressions.

Press down with both hands directly over the breastbone to perform a compression, which helps the heart beat. You should press down by about 2 inches (5 cm).

Chest compressions are more critical for correcting abnormal heart rhythms (ventricular fibrillation or pulseless ventricular tachycardia). Do the compressions in a relatively fast rhythm. Some agencies recommend doing compressions to the beat of the chorus of "Stayin' Alive," a 1970s disco hit, or at roughly 103 beats per minute.

Continuing the Process Until Help Arrives

Minimize pauses

Minimize pauses in chest compression that occur when changing providers or preparing for a shock.

Attempt to limit interruptions to less than 10 seconds.

Make sure the airway is open.

Place your hand on the victim's forehead and two fingers on their chin and tilt the head back to open the airway.

If you suspect a neck injury, pull the jaw forward rather than lifting the chin. If jaw thrust fails to open the airway, do a careful head tilt and chin lift. If there are no signs of life, place a breathing barrier (if available) over the victim's mouth.

Give two rescue breaths (optional).

If you are trained in CPR and totally confident, give two rescue breaths after your 30 chest compressions. If you've never done CPR before, or you're trained but rusty, stick with only chest compressions.

Repeat the cycle of 30 chest compressions.

If you're also doing rescue breaths, keep doing a cycle of 30 chest compressions and 2 rescue breaths.

You should do CPR for 2 minutes (5 cycles of compressions to breaths) before checking for signs of life.

Continue CPR until someone takes over for you, emergency personnel arrive, you are too exhausted to continue, an AED is available for immediate use, or signs of life return.