| Last updated
A video shot at the scene by fellow shopper Zoey Thornton shows the rescuer breaking the window before letting the dog out of the passenger side door so it can breath cool air once again.
The 29-year-old claims the dog was in the car for 'at least 30 minutes' on Sunday afternoon.
Zoey said that before they broke the car window through, they tried to contact the owner of the car by asking Tesco, Home Bargains, and Poundland to put out a call on their PA systems urging the owner to return to their vehicle.
She said that she became involved in the incident when she saw a woman in the car park looking concerned and went over to see what was going on.
Zoey explained: "We went over to see if everything was alright and it turns out that the dog was inside, it was really hot.
"The window was open a little bit but we were there for at least half an hour before any action was taken.
"It's long enough for a dog to overheat in a car."
After the man released the dog from the car they tried to give it some water, and then reported the incident to South Wales Police.
Zoey continued: "We made announcements in Tesco, Home Bargains and Poundland for the owner to come out to the car but no one came out. We phoned the police and they turned up before the owners arrived.
"The dog was panting quite heavy. The people who noticed it first of all said they were there for a good 10 to 15 minutes before we got there.
"We smashed the window just before the police had arrived as it was starting to get too long.
"We just thought that was the next option as the car was getting hotter.
"I've got dogs myself and I wouldn't leave them in the car. I just want people to be aware not to leave their dogs in the car in hot weather."
A spokesperson for South Wales Police said: "We received reports about a dog in a car at Fforestfach at about 2.30pm on May 31.
"Officers attended and the dog had already been released from the car. The owner was located and given advice.
"We would like to remind people that dogs can die in hot cars."
If you see a dog in a hot car - and you can't find the owner - call 101 or, in an emergency, 999.
Chosen for YouChosen for You
Most Read StoriesMost Read