Pittsburgh police responded to 10 heroin overdoses, which resulted in two deaths, within a 24-hour span.

Five of the overdoses occurred within five hours Tuesday evening. Police were called to another overdose-related incident Wednesday morning.

According to Pittsburgh police Cmdr. RaShall Brackney, officers were dispatched to incidents reported between 3 and 8 p.m. Tuesday.

Brackney said three of the victims responded positively to on-scene medical efforts, but the other two were taken to UPMC Mercy Hospital, where one died and another was admitted in critical condition.

Paramedics gave the victims Narcan, a drug overdose antidote.

A second overdose victim died Wednesday afternoon, according to TribLIVE.

Patrick Byrnes, 38, of Beechview, and James Nardozi, 31, of Dormont, died of suspected overdoses Tuesday. The cause of death for both men is pending, Allegheny County spokeswoman Amie Downs said to TribLIVE.

"My mom called me hysterical, and she was crying and said, ‘He's gone,’" said Billy Nardozi, James Nardozi’s nephew.

Billy Nardozi said that his nephew was trying to stop using.

"We'd say, ‘Oh, he's getting off of it. He's going to be fine.’ And then I don't know what happened,” said Billy Nardozi. “He cared for people. He was a wonderful person."

Police said another person overdosed on heroin Wednesday morning, and crashed into a fence on Mount Troy Road in Troy Hill.

"He was passed out, slumped over the wheel," said Jim Ritenour, who lives nearby.

That man was also revived with Narcan, officials said.

Police believe that drug dealers are selling a stronger version of heroin. TribLIVE reported that stamp bags with the word "predator" and a photo of a shark were found at three of the scenes.

"We understand this is a competitive market and drugs get strong and stronger, but heroin right now is very potent and very deadly," said Brackney.

Brackney said the department’s resources have been overstretched in the past 24 hours, and unless they can find the source and discourage people from using it, the 10 overdoses may just be the beginning.

“At this point in time, we are trying to determine the routing system as well as the distribution system for the drug,” Brackney said.

Narcotics agents said they can’t yet say with what the stamp bags of heroin might have been laced until test results come back from the lab.

“It is true there are intentional situations where a hot shot is put in the bag. However, it could be accidental. They could be trying to strengthen it,” said Vanessa Sebetich, marketing director of Greenbriar Treatment Center in Wexford.

Sebetich said she’s a big proponent of Narcan, the antidote used to revive at least four of the recent heroin overdose victims, but added that it should not be viewed as a crutch or an excuse to keep using.

“The reality is, what folks in addiction fear more than anything is the withdrawal. Yes, (Narcan is) a lifesaving drug, but it puts them into immediate withdrawal,” she said.

Pennsylvania is one of 24 states that allows Narcan to be used.