Hello Algates, this is really a very good question because as you said, most of the time people are alone when they get the heart attack. I came across some first aid information for this situation thats what I have given here.
Usually, the people who is having heart attack with get improper heart beat, severe pain in the chest and then the pain will move on their arms and withing 10 seconds they will be unconscious.
So within that 10 seconds, if they identify that as heart attack then they should start coughing continuously and heavily. Between that coughs, they should have deep breath. They should do this continuously until they get some help or they reach hospital or their heart beat become normal.
Cough is really helping at this situation to squeeze the heart which will help to pump the blood circulation also it helps to bring the heart beat back to normal.
Deep breathing will help the person to get more oxygen for lungs.
This information is provided by some Cardiologist. So, I hope this should be helpful for lot of people.
PS: I am NOT a doctor or NOT a person from medical background