A family has been left heartbroken after two of their pet dogs died and another was seriously injured following a deliberate poisoning near Geelong.

Dog owner Samantha Blackley said she and her husband returned to their home on Sunday morning to find the family's four-year-old kelpie, Bindy, and five-year-old border collie, Buddy, dead in the back yard.

Their 10-month-old great dane, Duke, was convulsing, vomiting and near death.

"I was inside and he was calling out to me 'Sam, Sam the dogs are dead, get out here'," she told 7News.

"I ran outside and he asked me to get the car.

"It was a horrible sight - I wouldn't wish it on my worst enemy."

Samantha, who is five months pregnant, had no other choice but to bundle Duke, who weights 65kg, into the back of the car and race to the vet.

Once there Dr Robyn Blackwell discovered a stimulant inside the dog.

She said the dogs had been deliberately poisoned, although the exact type of stimulant used is still unclear.

"Most poisonings are accidental....but this doesn't seem like it was an accidental poisoning," she told 7News.

"To have three dogs poisoned in such a short time is not good. There's no known toxins in that house."

The young family say they are in disbelief and can't understand why anyone would want to hurt their animals.

"I don't understand how anyone could be so low...it's just disgusting," Samantha said. "If they could do this to an animal what could they do to humans?

"Yeah they bark, but they bark to protect our property, they're not nuisance barkers."

Police are investigating the incident.

Meanwhile it's a long road to recovery for Duke, who is now recovering at home.

"We're very lucky he doesn't have brain damage," Samantha said. "His temperature when he got in to the vets was deadly."

It could have been much worse, Samantha said, if her 20-month-old son Jack had been in the backyard.

"If he had picked up whatever it was that the poison was in and I hadn't been able to wash it off he might not be here," she said.