Contaminated meat laced with toxic liquid and metal pins has been planted throughout Canons Park to poison dogs, according to police.
Two are seriously ill after eating the meat, believed to be pigs' hearts, which were found in shrubbery on the east side of the park in Edgware.
Boomer, a yellow Labrador, was rushed to the vet on Thursday last week where he underwent an emergency operation to remove 67 embroidery pins riddled throughout his body.
A relative of Boomer's owner had taken the two-year-old out for a walk when he noticed the meat and pins sticking out of his mouth.
His owner Edward Birch is horrified someone could carry out such a cruel act. He said: "I am pretty disgusted and sickened at the moment. It is just an unbelievable thing to do.
"The vets managed to remove 67 pins but there is still one stuck inside him.
"It really was touch and go. We thought we were going to lose him. One minute he was so lively running around and the next he is being cut open on an operation table. It is sick."
Police confirmed another dog was recovering after eating another piece of an animal's organ covered in poison and that another had been found, again filled with pins.
Mr Birch said: "This was a deliberate attack carried out by someone who doesn't like dogs. I hope other owners are more cautious when walking their dogs in the park."
An investigation has been launched by Canons Park Safer Neighbour-hood Team to try to discover who is planting the slabs of contaminated meat.
Officers are keen to question a slim Asian man in his 20s who has been seen verbally abusing dog owners in the park, but no one has been arrested.
PC Chris Rayment said: "We have had reports of an Asian man wearing a tracksuit running around the park and being aggressive towards dog owners.
"People should be taking extreme care when in the park with their dogs. Three pieces of meat have been found already. We are not ruling out the possibility that more pieces may be planted when the weather clears up. We will continue to search the park and increase patrols of the park."
The officer said owners should keep their pets on leads and keep a close eye on things they put in their mouth. Parents should also make sure they do not leave their children unattended.
He said: "We believe we are dealing with someone who has a vendetta against dogs. If anyone sees anything suspicious they should report it to the police straight away."
If anyone has any information call Canons Safer Neighbourhood Team on 020 8721 2995.