A DOG walker whose fatal mistake saw a client's pet die in a hot car, sent a text message to the owner when she realised what had happened.
The dog was found dead by its female owner inside the car where it had been for about six hours, Nine News is reporting.
The owner contacted the dog walker after her pet was not returned home and received a text message saying: "I'm really sorry, I think I left your dog in my car".
A passer-by helped the distraught woman smash a window to retrieve her pet.
"He was rigid and still as a plank," Glenn Herne told Nine. "His fur came out in my hand when I lifted him up. He was falling apart. The car was very small, warm and smelly so I put him on the grass."
It is unclear where the walker was at the time but it's believed they may have left on a cruise shortly after parking the car.
NSW Police said a four-year-old dog was left inside a parked car on Tuesday afternoon on a Rose Bay road in the city's affluent east.
The dog was in the care of a walker at the time, and its female owner, 46, became concerned when her pet had not been returned home, police said.
The woman located the car about 5.30pm to find her dog had died.
Both the RSPCA and police were notified, and officers from East Suburbs Police Area Command are investigating the incident.
On the NSW Police Force Facebook page, comments have been damning of the dog walker.
"You had one job," one person wrote.
"Here's a good case for name & shame. other people are putting their trust in this person," another commenter said.
In a statement sent to news.com.au, police urged the public never to leave pets in cars on hot days after the incident.
"As the weather heats up, police are reminding the public that not only is it an offence for children or pets to be left unattended in vehicle, even with the air conditioning on, but it can be deadly," the statement said. "Anyone who finds a child or pet located in a vehicle should call triple-0 (000)."
People should be on alert over the next few days as a nationwide heatwave sends temperatures soaring. Parts of western Sydney are expected to reach 40C this week.