The woman said she thought the driver might be someone she knew pulling a prank, but she got out of the way of the vehicle when she saw who was sitting in the driver's seat -- a dog.
The car crashed into the store at a slow speed and came to a rest.
A second dog in the passenger seat of the car somehow managed to roll down a window after the crash, the woman said.
She said the owner of the car, an elderly woman, was paged to the front of the store. The owner said she had left the car running so the air conditioning would safeguard the dogs from the summer heat.
A Walmart employee said damage to the car and building was minimal. The dogs were not injured.
The car was in good enough condition to drive away from the scene, witnesses said.
The doggie driver was far from the first canine to get behind the wheel -- a Yorkshire terrier in Ellsworth, Maine, was rescued from Branch Lake last fall when he knocked his owner's pickup out of gear and the vehicle rolled straight into the water.