Officials said the 3-month-old, mixed-breed pup was rescued by an animal services officer who forced open the van door in a Walmart parking lot in Riverside, the Los Angeles Times reported Thursday.
The windows inside the van were cracked open, but "it was still too hot for that little dog," Riverside County Animal Services Officer Will Luna said.
The temperature in Riverside on Thursday topped out at 101 degrees, the National Weather Service said. The area is under excessive heat watches and warnings through the weekend.
The pup, named Sheri, was taken to an animal shelter in Jurupa Valley, where her temperature registered 103.7 degrees, the Riverside County Department of Animal Services said.
The dog was stabilized and returned to its owner, the Times said.
"Since the dog did not die," department officials said in a statement, "the woman was cited for leaving a pet inside a car unattended."
The citation costs $124, officials said.