A2A.
By heart attack,I presume you mean “Acute coronary syndrome”. (There are conditions that can mimick symptoms of heart attack).
I will restrict my answer to emergency management of Acute heart attack aka Acute Coronary syndrome.
Broadly there are three types of Acute heart attack or ACS.
  1. Unstable angina
  2. NSTEMI (Non- ST elevation MI)
  3. STEMI (ST elevation MI).
There are some differences in management for each, however in my answer I will address what a layman person should do in case of suspected heart attack.
Identify the symptoms to know that it's heart attack-
Palpitations,
Pain, which is usually described as pressure, squeezing, or a burning sensation across the chest and may radiate to the neck, shoulder, jaw, back, upper abdomen, or either arm.
Breathlessness,even at rest.
Diaphoresis i.e. excessive sweating (enough to cause drenching of clothes)
Nausea
Rarely there can be atypical symptoms (especially in diabetic patients and females), heart attack can cause symptoms mimicking heart burn ,giddiness, fainting attack etc.
Once you suspect it's a heart attack-
Immediately stop any physical exertion.Make the patient lie down.Provide enough air and most importantly call an Ambulance to take the patient to nearest medical emergency.Time to starting treatment affect survival.The more is the delay,the more is the risk of death.
Now,there can be two scenarios -
1). Patient is already a known case of ischemic heart disease (CAD- Coronary artery disease)
In this case,most patients would already be on meds.If there are meds at home.Immediately give the following-
Aspirin - 300 mg-(75 mgx 4 tablets),to be chewed
Clopidogrel - 300 mg
Isosorbide dinitrate - 1 tablet to be placed below tongue- can be repeated every 5 minutes,for 3–4 doses,if pain is persistent.
Atorvastatin -80 mg.
Morphine if available - 10 mg tablet- can be repeated in 15 minutes,if persistent pain.
All these medications should be given immediately at Start of symptoms,if available. ( All of them together- don't waste time thinking- so many tablets- they are saving your patient's life).
2). Patient is not a known case of heart disease and you don't have tablets available at home.
Don't waste time arranging/buying medicines.Immediately rush the patient to nearest emergency centre to start the treatment at the earliest ( patient must be resting all this while- lying down/sitting,try to minimise physical exertion which will further increase the severity).
Hope that helps.