Check the pulse in the neck. If there's no pulse, then you would do cardiac compressions. The combination of chest compressions and rescue breathing bring oxygen to the brain until the defibrillator arrives. Some people might be concerned about infectious disease, AIDS, hepatitis, that if they come upon a stranger and give help, they're putting themselves at risk. That is the most common question asked in a CPR course.
People are concerned.
If they're very concerned about it, they can carry a face shield or a pocket mask. A pocket mask can be kept at work, a face shield, you can carry it literally in your pocket or in your pocketbook. This creates a barrier between you and the patient so no body fluids can touch you and also decreases the concern a person may have. The American Heart Association has over 5,000 training centers in the United States. Just call your local Heart Association.