This is the real killer condition. If medical help is not provided within 30 minutes of the onset of a heart attack (sometimes even 60 minutes), 60 to 65% of patients are likely to die. 

Even today - in the USA - 60% of patients do not reach the hospital in time for treatment.

In other words, modern medicine has concentrated all attention on the lucky 40% who manage to reach the hospital after suffering a heart attack, leaving the vast majority, 60 to 65%, to suffer or to die unattended.