Heart attacks are a common cause of death. While nothing may be able to prevent an impending heart attack, a quick course of action from a bystander may help prevent death. Take immediate steps if someone thinks they are having a heart attack or you witness a heart attack happen, usually evident by sudden collapse.
Call 999 / 112. If you are in a public place, send someone to locate an automated external defibrillator (AED) if one is available in the local area. The automated external defibrillator is a portable shock system which analyses heart rhythms and advises if a shock is necessary. During a cardiac arrest, the heart may establish an irregular beat which only an electrical shock can regulate. If you have started CPR and someone arrives with an AED, follow the directions on the machine. It will tell you exactly what you need to do until help arrives.
Check the victim's airway, breathing and circulation if the victim has collapsed. Provide CPR as necessary. If you have access to an AED, use it. After you connect it to the patient, following directions on the machine, it will tell you if a shock is advised or if you just need to keep doing CPR. If you follow the directions, you can't go wrong.
Give the victim an aspirin tablet (unless he cannot take aspirin due to a contraindication with his other medications) if the victim has not collapsed and is still awake and aware of his surroundings. Get the victim to chew the tablet or let it dissolve under his tongue.
Remain calm. Keep the victim calm by reminding him that you are there to help and that emergency help is on the way.
Use oxygen, if available and if trained to use it. It will help the victim breathe better and more efficiently by using less energy to do so.
Continue to assess the victim until the emergency team arrives. If at any time the victim suddenly stops breathing, re-assess the situation and provide CPR as needed.