Now, Heidi, an eight-and-a-half year old Shepard-Lab mix, is credited with saving yet another life: Her owner's.
"She's saved a lot of lives," Wills said. "I just never thought she would save mine."
Wills had no symptoms of cancer, but in February, Heidi started acting differently around her. The dog started pawing at her owner's arm constantly.
"She (was) progressively getting more aggressive with that behavior, and then she started taking her nose and burying it in my chest and sniffing very, very hard," said Wills.
She told her doctor the story, and he sent her in for a CAT scan.
“The next morning he was calling me telling me that he sees three spots of what looks like cancer,” said Wills. “It was right where Heidi was smelling my chest.”
Doctors told her Heidi’s warning most likely saved her.
“When they come (after) they develop symptoms, which is usually when we first see them, they typically already have advanced stage lung cancer that isn’t curable,” said Dr. Enser Cole, Wills' oncologist and chief of Medical Oncology at Saint Agnes Hospital.
Wills' cancer is in remission now.
"Listen to your pet, your dog," she said. "Not saying every dog, every time they smell you, it's something bad, but if you see something like my situation, at least, stop and think, 'Should I go to the doctor?'"
It's unclear exactly how Heidi knew about Wills' condition, but Cole said researchers hope to discover the chemical that dogs smell when cancer is present soon.