The mother of the men, named locally as Kevin and Peter Moran, became concerned after they had not made mobile phone contact for a number of days and was present when the grim discovery was made.
She had gone with a caretaker to check on their apartment in Steamboat Quay at about 3.30pm.
The men, who were in their mid-20s, originally came from the Old Cork Rd area of the city.
The double tragedy sparked fears last night for hundreds of heroin addicts in Limerick, as gardaí confirmed they had received information that a contaminated batch of heroin had hit Limerick in the past week.
A source said: “The fact that the twins died at around the same time in the same place using drugs from the same source adds to the suspicion that they had used contaminated heroin.”
After a preliminary examination of the apartment, gardaí said they were not treating the deaths as suspicious.
A Garda spokesman said last night that, as a procedural matter, Detective Inspector Tom O’Connor, who was leading the investigation into the tragedy, had called in the state pathologist to carry out an autopsy today at the Mid-Western Regional Hospital. Toxicology tests will show if contaminated heroin caused the deaths.
A recent study by the Mid-West regional drugs taskforce showed that the Limerick area had the worst heroin problem in the country outside Dublin. About 280 heroin addicts are on supervised methadone treatment in the city to help them go clean.
Addiction counsellors say hundreds more are actively taking the drug.
Gardaí attribute a huge spike in the number of break-ins to houses in Limerick over the past two years to heroin addicts desperate for money to feed their habit. During the first three months of this year over 300 houses were broken into in the city. Many of these crimes were carried out in the suburbs, many during daytime.
The McCarthy-Dundon gang is a major player in the sale and supply of heroin.
As well as Limerick, the gang’s drugs network spreads through Munster and into the West of Ireland.
Although many of the gang leaders are currently serving prison sentences, their heroin business is undiminished. A relative who returned to Limerick about two years ago from London controls their operations in Limerick.
Another long-time associate, who was jailed for drugs offences on the Continent, now lives in the Limerick area and is believed to have strong links with major heroin players in Cork.