Fisrt action if you see someone having Heart attact

A heart attack occurs when an artery supplying your heart with blood and oxygen becomes blocked. This loss of blood flow injures your heart muscle. A heart attack generally causes chest pain for more than 15 minutes, but it can also be "silent" and have no symptoms at all. 

Many people who suffer a heart attack have warning symptoms hours, days or weeks in advance. The earliest predictor of an attack may be recurrent chest pain that's triggered by exertion and relieved by rest (angina). 

Someone having an attack may experience any or all of the following: 
Uncomfortable pressure, fullness or squeezing pain in the center of the chest. The pain might last several minutes or come and go. It may be triggered by exertion and relieved by rest.
Prolonged pain in the upper abdomen.
Discomfort or pain spreading beyond the chest to the shoulders, neck, jaw, teeth, or one or both arms.
Shortness of breath.
Lightheadedness, dizziness, fainting.
Sweating.
Nausea.

If you or someone else may be having a heart attack: 

Dial 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. Police or fire-rescue units also may be a source of transportation. 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.

Chew and swallow an aspirin, 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. 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 proceeding directly to chest compression. The dispatcher can instruct you in the proper procedures until help arrives.