The RSPCA has condemned a woman who threw an elderly dog out of a car window tied in a black plastic bag.
A dogwalker who witnessed the incident near Merthyr Tydfil opened the bag and found a Staffordshire bull terrier between 13 and 16 years-old.
An examination found the animal had stomach cancer and had to be put down because of her poor condition.
RSPCA inspector Gemma Cooper said it was a "callous and utterly unacceptable" behaviour.
"This was a dreadful way to treat an animal, especially an elderly, sick dog."
"It is likely that the owner could not afford medical treatment but this behaviour is callous and utterly unacceptable.
"We need the public to help find the person responsible for this outrage."
The animal charity are appealing for information following the incident on Wednesday, 16 February at about 1830 GMT in an area known as the old pit site, near Crescent Street, Merthyr Vale.
The animal was examined by a veterinary surgeon who discovered that she had stomach cancer, an enlarged heart as well as other signs of neglect.
The member of the public was unable to identify the car model or its registration number.
Anyone with relevant information is asked to call the RSPCA on 0300 1234999 in confidence.