Unfortunately, more than 350,000 such emergencies a year don’t occur in that optimal place. In medical jargon they’re called Out of Hospital Cardiac Arrests.

Of people suffering these, only 46% get the immediate help that they need before professional help arrives. As a consequence the mortality rate for out-of-hospital cardiac arrest is 90%, according to the American Heart Association.

The likelihood of being among those who get immediate help needed for the best chance of survival depends on the location outside a hospital. 70% of the time it’s at the person’s home or someone else’s residence, while 11% occur at nursing homes. Those are places where a susceptibility to heart trouble might be known and some degree of preparation made.

The other 19% of Out of Hospital Cardiac Arrests occur in public settings, where getting the immediate help that doubles or triples their chance of survival depends on the reaction of bystanders.

Such was the case just before Christmas for a customer of a Millville Wawa, who collapsed into unconsciousness about 10:30 p.m. in the women’s room. When a fellow customer alerted the staff, a high school senior working the deli counter knew what to do and took action.

John Wallop ran to the bathroom and found the women not breathing and turning purple. He instructed his coworker to call 911 for help and immediately began CPR on the woman.

The woman started breathing … but then stopped again and had no pulse. Wallop, 19, of Millville, said she “died on me” for a couple of minutes, but he kept giving her CPR and she came back to life, breathing again. He got her upright and two women stayed with her until paramedics arrived and took her to the local hospital.

About half of Americans say they know how to perform CPR, but only 11% have the familiarity with its details that comes from current training, according to a new Cleveland Clinic survey. The recommended technique for bystander CPR consists of just chest compressions — and no breaths — on an adult. These compressions should be performed rapidly, 100 to 120 beats per minute.

And while most Americans know to call 911 as the first step in responding to a heart attack, only about one-third know that those suffering one should chew an aspirin right away.

John Wallop took his CPR class during a summer visit with his grandmother in North Carolina. A nurse, she was taking the class as part of her job and he thought it would be a useful skill to learn. His first chance to use it more than confirmed that.