If you think you are having a heart attack, firstly ensure you have called for emergency help.
But while you are waiting for help to arrive, taking aspirin can lessen the damage caused by the heart attack due to it being a blood thinner.
You should take 300mg of crushed, uncoated aspirin to enable the fastest results.
However, if you are allergic to aspirin, don’t take it, even if you are having a heart attack.