When Heather McNutt came home Sunday night, Milo wasn't his typical, chipper self. Instead of leaping off the chair to greet his human, he ignored her calls to come. Heather went to Milo instead and when she picked him up, he went limp in her arms.

Milo wasn't interested in the water McNutt offered him and he attempted to eat the treat she gave him but lost interest quickly. Heather put Milo in the car and carried him to Emergi-Vet.

After his examination, Milo's temperature was 92, ten degrees below the average 102 for dogs. His blood sugar was low and he was started on glucose. Heather left Milo with instructions to return the following morning at 6:30 to transfer him to his regular vet.

When Heather arrived, she was taken into a room and found the vet holding Milo in her arms. He was struggling to breath.

'He's not going to make it,' the doctor said. Milo's body was shutting down and, unwilling to watch him suffer anymore, Heather made the heartbreaking decision to put him to sleep.

What the vet believe killed Milo may surprise you and this deadly substance is more toxic to dogs than chocolate. Odds are it's also in your home right now.

Xylitol is a by-product commonly found in many fruits and vegetables. In the past decade, the natural sweetener has risen in popularity and so has the occurrence of death in dogs who consume it.

Xylitol is difficult to avoid. The ingredient is commonly used in diabetic and diet foods, sugar-free gums, even toothpaste. You can find a list of other products here but the list is by no means exhaustive. Be safe and check the label.

Heather wanted to make sure pet-owners were aware. "Maybe their fur babies can avoid suffering like Milo did,' she said.