Five new kittens which were found shut in a suitcase in temperatures approaching 32C (90F) are being cared for by animal welfare officials.
The abandoned litter of three-week old kittens - and their mother - were found by youngsters near the new PDSA pet hospital in Southend, Essex.
The youngsters said a middle-aged man had asked them to look after the case - then vanished.
PDSA officer Shirley Morris said: "It was despicable thing to do.
"Left another hour the kittens would have died an agonising death suffocating in the heat."
Hospital staff, who cooled down the cats and gave them fluids to rehydrate them after their ordeal, are now looking for new homes for them.