What can you do when a person is going into cardiac arrest?

If someone is about to have a heart attack and the ambulence is on the way, what can you do?
What can you do to help the person before the ambulence is there?
Scientifically speaking.

CPR. Check out the Red Cross' web site for more info:

Take CPR to learn what to do before it happens.

PRAY PRAY PRAY TO THE LAWD

Cardiac arrest is what happens when a person dies. The heart does not beat and breathing ceases, which starves the body of oxygen. Sometimes a person can be revived during the first several minutes after cardiac arrest. However, the more time that passes, the less likely it is that the person can be revived and, if revived, the more likely it is that brain damage will have occurred. Brain damage is likely if cardiac arrest lasts for more than 5 minutes, and death is likely if cardiac arrest lasts for more than 10 minutes. Fewer than 5% of people who are not already hospitalized when they have a cardiac arrest survive to be discharged from the hospital, and many survivors have brain damage.

A person in cardiac arrest lies motionless without breathing and does not respond to questions or to stimulation, such as shaking. A rescuer who encounters someone who fits this description first determines whether the person is conscious by loudly asking, "Are you OK?" If there is no response, the rescuer turns the person face up and uses the "look, listen, and feel" approach to determine whether breathing has stopped
First aid for cardiac arrest should proceed as quickly as possible. An automated external defibrillator (AED鈥攁 device that can start the heart beating again) should be used immediately if available. The next step is to call for emergency medical assistance. Next, if the person has not resumed breathing, cardiopulmonary resuscitation (CPR) should be started. CPR combines artificial respiration (mouth-to-mouth resuscitation, rescue breathing), which supplies oxygen to the lungs, with chest compressions, which circulate oxygen to the brain and other vital organs by forcing blood out of the heart.

CPR only if they stop breathing (take a course before trying to perform this).

Aspirin (three baby aspirins) is a good idea. I keep a bottle with me in my purse just in case (it has happened to me and that is what the EMTs did as soon as they got their hands on me).

Learn CPR before you need it.

Most heart attacks will not require CPR. The patient is in pain or discomfort. You can help them into a position where they feel less discomfort. You can provide reassurance, since one of the symptoms of a heart attack is fear - dread.

If they have cardiac medicine, like nitro, you can help them take it if that's what they want to do. Very often the 911 operator will have instructions for you, as well.

You can turn on an outside light so the ambulance can find you. You can move furniture away from the door and hall, and clear a path for the gurney and the EMT's. If the walk needs to be shovelled, do it. Put salt down on ice on the walk or drive.

Call the patient's doctor and let them know what's happening. He or she may have instructions for you.

Well, if they aren't unconscious, I wouldn't do CPR. Some people who have had a previous myocardial infarction (a.k.a. heart attack or MI) will often carry a small pill holding device on their key chain; it will contain a small pill of nitroglycerin. You can slip this under their tongue and it will temporarily dilate their blood vessels, which should help (...it's why they have the pill).

If they pass out, CPR can be used to help oxygenate, and more importantly, circulate their blood.

Well. if the ambulance is on the way, you can make sure they are breathing and if they are not give them rescue breaths. If their is an automatic defibrillator present you could hook them up to it. Offer them an aspirin if you have one in your purse or pocket.
If they arrest while your waiting on the ambulance, you could give them a big WHAM! on the chest and start CPR.

CPR.

CALL 911 and perform CPR.