Fifty-four-year-old Nigel, who returned to the store to thank Gayle after being released from hospital, said: "Gayle has given me a second chance; she saved my life.
"There is no thank you big enough to say to her.
"She just jumped in and did what she had to do to save my life before the ambulance crews got there.
"Some people may have panicked but not Gayle. She went above and beyond. I will be eternally grateful to her."
When Nigel collapsed by the checkouts, Gayle rushed over to help while a customer called 999.
As the situation worsened Nigel stopped breathing and he became unresponsive.
Thirty-eight-year-old Gayle, who's worked at the store for three years, said: "When Nigel stopped breathing I told the customer who was on the phone to the 999 team that I was commencing CPR.
"The ambulance team asked if we a defibrillator and I said 'yes' and they asked me to put it on him so it could monitor his heart.
"The defibrillator kept analysing his heart rhythms and continued to tell me to keep doing CPR and then it said shock required so we stood back and then continued CPR.
"At this point he still wasn't breathing.
"We carried on, really determined, and then there was a lady there who was a carer who jumped in for me at the very end and did three or four compressions and he started to take gasps for air.
"There was just sheer relief when he started to breathe again and the paramedics arrived at that point."
More than 600 Asda stores are equipped with a defibrillator.
"I'm not first aid trained, but I have picked things up and I was taught things from my late mum, Jill, who was a nurse.
"We used to watch TV programmes such as 999 so obviously I'd absorbed things without really knowing.
"I also knew that you had to do CPR to the rhythm of Stayin' Alive and I did that in my head.
"I didn't have time to think about it – I just did it.
"I haven't done anything special, I just did what anyone else would have done in that situation.
"I was just in the right place at the right time. It was such a shock as one minute he was there and the next minute he wasn't."
Gayle, who's married to Carl and has three children, said she was so relieved that Nigel had now recovered and is doing okay.
She said: "He's so thankful, bless him.
"When he came in to see me he told me that when he had his angiogram he was told that person who had done the CPR on him had done a very good job. So I'm proud of that.
"He always come to see me when he comes into the shop now."
Nigel, an HGV breakdown support specialist who lives a ten-minute walk away from the store, said: "I don't remember any of it at all, only what I've been told by Vicki, Gayle and the store manager Justin McRae. They have been filling in the blanks.
"All I remember is standing in the queue for self checkout and the next thing I was in Doncaster Royal Infirmary.
"I'd like to thank everyone at the store and the customers who helped me and looked after Vicki on that day."
Justin, who nominated Gayle for an Asda service superstar award, says all colleagues are proud of her.
He said: "Gayle did not hesitate at all when it came to performing CPR and following instructions from the emergency services.
"The lead paramedic returned to store to tell me that without Gayle's intervention and actions it was highly unlikely that the gentleman would not have made it. She had given him the best possible chance of surviving
"What Gayle did was brilliant and incredible – she saved a person's life! Not all superheroes wear capes; this one wears green! The team here at Rossington and myself are all in awe of what Gayle did."