Bev Seel, 41, had popped into M&S in Aintree to take advantage of a gold voucher promotion on its first day of business.
But instead of a gold star she found an elderly man going blue after getting a free sample of steak stuck in his throat.
Bev, who grew up in Anfield, said: When I came across him he was in big trouble. By the time the paramedic would have got there he would have stopped breathing.
He was turning blue and had lost consciousness. I tried slapping him on the back but it wouldnt budge so I tried abdominal thrusts what used to be called the Heimlich manoeuvre to dislodge the blockage. He started to breathe again and regained consciousness.
Bev, who studied nursing at the Royal Liverpool hospital, said: When the paramedic did arrive he turned to the mans daughter and said I had saved his life. Ive saved lives before but only in work, never on the floor of Marks and Spencer!
Bev, who went to Anfield Road Primary, and Stanley Park Comprehensive, is a member of the British Red Cross attending events at the Echo Arena, and the Grand National to make sure people have medical care.
She said: When I used to go out all the time in town youd see people getting into fights and youd stop to help them when they got hurt, or youd stop at car accidents to see what help you can give. It just becomes second nature.
I never did find my gold star but Im glad I found an even greater reward in saving a mans life!
A Marks & Spencer spokesperson said: We're delighted our customer has made a full recovery and we're grateful that Mrs Seel was on hand to provide assistance on the day.
