Chest pain has other causes such as indigestion, heartburn and pulled muscle. But unless the cause is obvious from symptoms or history, treat as possible heart attack. Someone having a heart attack may experience any or all of the symptoms:
May or may not have actual chest pain but may experience any of the following:
Pain radiating down the left arm (sometimes the right or both arms)
Uncomfortable pressure, fullness or squeezing pain in the center of the chest
Prolonged pain in the upper abdomen
Discomfort or pain spreading beyond the chest to the shoulders, neck, jaw, teeths
Shortness of breath
Lightheartedness, dizziness, fainting
Sweating
Nausea
A heart attack occurs when an artery supplying your heart with blood and oxygen becomes partially or completely blocked. This loss of blood flow injures or destroys part of your heart muscle. A heart attack generally causes chest pain for more than 15 minutes, but it can also have no symptoms at all.
Many people who experience a heart attack have warning symptoms hours, days or weeks in advance. The earliest warning sign of an attack may be ongoing episodes of chest pain that start when you're physically active, but are relieved by rest.
If you or someone else may be having a heart attack:
Call 911 or your local emergency medical assistance number. Don't tough out the symptoms of a heart attack for more than five minutes. If you don't have access to emergency medical services, have a neighbor or a friend drive you to the nearest hospital. Drive yourself only as a last resort, if there are absolutely no other options, and realize that it places you and others at risk when you drive under these circumstances.
Make the individual as comfortable as possible. If they feel more comfortalbe leaning up against a tree rather then lying down, let them do so.
Ask if on medication such as nitroglycerin tabs
Chew and swallow an aspirin (one 325mg adult tab) unless you're allergic to aspirin or have been told by your doctor never to take aspirin. But seek emergency help first, such as calling 911.
Take nitroglycerin, if prescribed. If you think you're having a heart attack and your doctor has previously prescribed nitroglycerin for you, take it as directed. Do not take anyone else's nitroglycerin, because that could put you in more danger.
Begin CPR (see CPR under First Aid Tips). If the person is not breathing or is making gurgling sounds consider CPR immediately. If you're with a person who might be having a heart attack and he or she is unconscious, tell the 911 dispatcher or another emergency medical specialist. You may be advised to begin cardiopulmonary resuscitation (CPR). If you haven't received CPR training, doctors recommend skipping mouth-to-mouth rescue breathing and performing only chest compressions. The dispatcher can instruct you in the proper procedures until help arrives.
References:
Heart attack: First aid  from the Mayo Clinic staff
Wilderness First Aid, Frank Hubbel, DO, 3rd Ed., 2014, ISBN: 978-0-9826539-7-5