Every day that dental receptionist Heather Hall comes into work she is thankful for two things – firstly, that she is still breathing and, secondly, for her colleagues.

If it wasn’t for them, she would be dead.

A year ago Heather had a heart attack at her desk at Highgate Dental Practice. She had no previous record of heart trouble and was fit and healthy at the age of 48.

Her heart stopped three times and she was in a coma for four days. She survived thanks to the CPR training the practice staff had received just two days before.

When dentist Dr Hugo Hagan and hygienist Sally Tucker heard a loud sound from the receptionist’s office downstairs, they rushed to see what had happened.

“Heather was slumped in her chair,” said Dr Hagan, who owns the practice in Highgate High Street. “We thought she’d passed out. We checked her vitals and there was nothing, so we realised there was a problem.”

The pair laid Heather down and began chest compressions.

It was in these crucial few minutes before an ambulance arrived that stopped Heather suffering brain damage or dying.

“Had we not had the training, we would have been at a loss,” Dr Hagan explained. “At the early stages, the most important thing is to keep the oxygen circulating around the body. We all worked like clockwork.”

Heather, who has two daughters and two grandchildren, is forever grateful that her colleagues knew what to do.

“It’s horrible to think what would have happened if I hadn’t come into work,” she said. “I wouldn’t be alive.

“I don’t remember what happened in between, only that I woke up four days later with my daughter leaning over me.

“I was so confused. I didn’t understand why she would be in my office.”

More perplexing, perhaps, was Heather’s first request.

Unable to speak, she motioned for a pen and paper and traced the word “bag?” to her family.

“I was wondering where my bag was!” says the now healthy 49-year-old, who is back at work after a six-month absence.

The British Resuscitation Council advises that doctors and dentists update their skills every year.

But since they saved Heather’s life, Dr Hagan and his team have brushed up on their training every six months at a centre in Highgate.

Roma Felstein leads Safe and Sound’s CPR training and emergency medicine courses.

It works with about 200 GP and dental surgeries across the capital.

She said of Heather: “If that happened on the street, she wouldn’t be alive today.

“The training isn’t just for doctors. Simple things, like what to do when someone starts bleeding – it could save a life.”