Increased irregular heart rate. Feeling of impending doom. The victims have a habit of dismissing heart attack symtpoms. It's not uncommon for them to attribute these feelings to indigestion or heartburn. So, the most dangerous symptom of a heart attack turns out to be denial.
Most victims die within the first few hours of an attack due to that.
Obviously, the sooner they get treatment the better their chances are of recovering, especially within the first two hours. Call an ambulance and have the victim lay down with their legs elevated. This is known as a shock position. If the victim is standing or sitting their blood volume goes downward worsening the predicament. Work with gravity instead of against it by getting their lower body above their heart.