They took no mercy on poor Percy, a $1 million lawsuit says.

A high-powered Manhattan duo’s beloved French bulldog died after heartless dog sitters let him overheat in the back of a van and then dumped him — to perish alone — at their Upper West Side apartment, according to the suit.

Bankers Laura Garner and Robert Hardon entrusted their 5-year-old pooch, Percy, to caretakers at Queens- based Doggie Love for one night in July 2009 while they were out of town, the suit says.

“From the instant I saw Percy . . . I knew he was the one,” a devastated Garner wrote in an affidavit, recalling the start of her love affair with her pet.

But that affection wasn’t shared by Doggie Love, says the suit filed by the couple in Queens Supreme Court yesterday.

One worker drove the dog — whose breathing and ability to regulate heat were already limited because he was a “flat-faced” breed — from Astoria to the couple’s apartment on West End Avenue in the back of an enclosed Econoline van, the suit says.

The employee then dropped off the obviously ailing Percy inside the empty apartment — despite the building’s doorman and a federal judge who lives next-door asking if they could get the dog water or call a vet, according to the papers.

Percy was discovered dead, splayed out in front of an air conditioner, a few hours later.

Vets examined Percy’s body that night and found evidence that his body temperature was “notably high” and he had suffered seizures, the suit says.

“The emptiness that has been left by Percy’s death and the anguish we suffered has not and will never be filled or go away,” the couple said in the lawsuit, which seeks at least $1 million in damages.

Doggie Love was initially sympathetic to their heartbreak but soon grew cold, with owner Nilo Mathias telling the couple that “sometimes, dogs just die,” the suit alleges.

Another owner, Marla Abrams, allegedly asked, “What do you want from us?”

Abrams yesterday told The Post: “The person in question no longer works for me,” adding, “I’ve always wanted to be a story in the New York Post.”

Mathias refused comment.

The company’s lawyer later released a statement saying, “Although the death of this dog is tragic, without an necropsy, the ultimate cause of death cannot be determined. We are confident that once Doggie Love has the opportunity to defend itself in court, it will be fully vindicated.”