A curious dog has had a lucky escape after swallowing a bag containing a deadly drug found buried in an Adelaide park.

Key points: Shelby swallowed the bag after a walk in a park

Shelby swallowed the bag after a walk in a park Denis and Kathy Parslow say the dog was in a "state of haze" after swallowing it

Denis and Kathy Parslow say the dog was in a "state of haze" after swallowing it Police say anyone who finds illicit drugs should contact them immediately

Shelby, a 16-month-old Cavalier King Charles Spaniel, often enjoys walks at the local park.

However, six weeks ago, owner Denis Parslow said a weekend walk at the park quickly became a $4,000 exercise.

"We were going back inside, and I noticed Shelby had something in his mouth, and it was rather large, so I challenged him and all of a sudden he swallowed it," Mr Parslow said.

"We went back inside, and he was fine. We went down to the beach that evening, having a great time and when we got back to the car he was totally flat, and he wouldn't jump out of the car.

"His eyes just weren't fixing on anything, and we didn't know what was happening at the time, but certainly, in fact he was just in a total state of haze in his eyes, as well as not eating and drinking."

Shelby the Cavalier King Charles Spaniel found the bag of heroin buried at a park. ( ABC News: Helen Frost )

On Monday, Mr Parlsow and his wife Kathy thought Shelby was getting worse.

He had started vomiting and looked like he was in pain so they took him to Torrens Road Vet Clinic, where he was treated for gastro.

However, the symptoms grew worse so they took him back the following day for x-rays.

Vet Jenny Weston said she was worried after the x-rays failed to show anything, so she asked whether she could operate.

"We went in and did an exploratory laparotomy and found a small bag of heroin in his stomach," Dr Weston said.

"Which was lucky, because the bag had caused pain but hadn't completely burst, so we were able to get the heroin out."

'They'll think we're doing illicit drugs'

Mr and Mrs Parslow said they were in "total shock" and could not believe what had happened.

"We were just thankful that it was identified, and it had been removed and he was going to be okay," Mr Parslow said.

Training tips from the vet: Teach your dog the command "leave it"

Teach your dog the command "leave it" Keep your dog on a short or long lead

Keep your dog on a short or long lead Use a muzzle to stop your pet picking up foreign objects

Use a muzzle to stop your pet picking up foreign objects Teach your dog to allow handling of the mouth to help with getting objects out

"I sort of shrieked because I thought, 'oh my goodness, they'll think we're the culprits and we're doing illicit drugs'," Mrs Parslow added.

"But, as you can see, Shelby doesn't look like the average drug mule."

Luckily, Shelby made a quick recovery and was able to go home the day after his operation.

However, as he had swallowed heroin, he received similar treatment to a person who had overdosed.

"They had to put him on Narcan to take away the effects of the drug that had been absorbed into his body," Mrs Parslow said.

"Of course, having had the operation he wasn't able to have opioid or opiate painkillers for helping with the recovery of his painkillers because he was in withdrawal."

Vet says owners need to be aware of dangers

Dr Weston said it was the first time she had ever treated an animal that had ingested drugs, but she did treat a lot of dogs who had eaten things they should not have, including corn cobs, Christmas decorations, socks, plastic bags, fishing hooks and children's toys.

She said she contacted the police after the grisly discovery.

Dr Weston said she has dealt with many dogs that had eaten the wrong things. ( ABC News: Helen Frost )

Now, Mr and Mrs Parslow want to make sure other dog owners are aware of the dangers and are not caught by surprise.

"The police sort of alerted us to the fact this goes on, they're not very surprised, that we would find, or that our dog would find something hidden, because often times dealers don't deal in front of their own house," Mrs Parslow said.

An SA Police spokesperson said anyone who finds anything they think might be illicit drugs, should contact them immediately.