Class A drugs worth more than £410,000 were discovered during a search of four homes and businesses in Renfrewshire and North Lanarkshire on Friday.
A significant amount of drug mixing agent was also recovered, which detectives said had the potential to boost the street value of the drugs to around £3 million.
A 32-year-old man was arrested after heroin and cocaine worth more than £250,000 and a firearm were found at a business in MacDowall Street, Johnstone.
Around £76,000-worth of drugs, mixing agent, firearms and cash were seized from a house in St Anne's Wynd, Erskine, leading to the arrest of a 42-year-old man.
A 55-year-old man was arrested after heroin with a street value of £93,000 was discovered at a house in Laverock Terrace, Chryston.
Mixing agent was also recovered from a house in Teviot Terrace, Foxbar, Paisley. The three men are expected to appear in court on Monday.
Detective Chief Inspector Kenny Armstrong, of Police Scotland's Specialist Crime Division, said: "This operation demonstrates our continued efforts in tackling serious and organised crime, and ridding our communities of drugs.
"Through effective intelligence gathering and the help and support from the public we will continue to deal with these issues head on."
Anyone with information about drugs in their community is asked to contact police on 101 or Crimestoppers on 0800 555 111, where information can be given anonymously.