A dog died in a car and three more were rescued from a van left in the heat at the Royal Show in Warwickshire.
RSPCA inspectors and police broke into the BMW car to try and remove the whippet but it had already died. The temperature inside the car was 47C .
The terrier dogs were removed from a van at the showground. RSPCA inspector Lee Hopgood said the incidents were being investigated.
"We cannot understand why we are still finding dogs in cars," he said.
'Irresponsible and illegal'
He said: "We are all devastated that a dog has lost its life because it was left in the sweltering heat of a car.
"It is irresponsible and illegal to leave a dog in a hot car."
People should not take their dogs with them when they attend summer shows, he added.
"Yesterday, we issued numerous verbal warnings to dog owners and my inspectors, who are patrolling the five car parks, cannot understand why we are constantly finding dogs left in cars."