Claudio Modini, director of emergency room at the Polyclinic Umberto I hospital, said: "James Gandolfini arrived at the emergency room of the emergency department of Polyclinic Umberto I University Hospital in a cardiac arrest accompanied by the ambulance of the 118 service."
"He was a code red [when he arrived]," Modini added, speaking in Italian.
"They were already trying to reanimate him. The efforts continued for 40 minutes, a series of attempts to make his heart start using electric activity.
"He died at 23:00."
Comedy writer and producer Armando Iannucci, who directed James Gandolfini in the 2009 film In The Loop, has paid tribute to the actor:
Gandolfini's role as Lieutenant General Miller in In The Loop was a contrast to his performances as mob boss Tony Soprano in the hit series The Sopranos.
James Gandolfini played Lieutenant General Miller in In The Loop, the 2009 black comedy film which followed the British political sitcom The Thick Of It.
Some of his most memorable moments feature language inappropriate for this website, but a cleaner contribution can be seen 39 seconds into the official trailer:
Simon Blackwell, one of the film's writers, wrote on Twitter: "Shocked and sad to hear of the passing of James Gandolfini. Great actor. Fond memories of working on In The Loop. Thoughts with his family."
Tributes have been pouring in for James Gandolfini, the US actor best known for his role in The Sopranos, who died of a suspected heart attack whilst on holiday in Rome.
Daybreak's Ross King reports on how the US reacted to his death:
James Gandolfini starred Tony Soprano in the HBO television series The Sopranos, which aired from 1999 to 2007. He won three Emmy awards and a Golden Globe for his portrayal of the conflicted mob boss.
Gandolfini and his wife Deborah, who were married in 2008, have a daughter Liliana, born last year, HBO said. The actor and his former wife Marcy have a teenage son, Michael.
New Jersey Governor Chris Christie said: "It's an awful shock. James Gandolfini was a fine actor, a Rutgers alum and a true Jersey guy. I was a huge fan of his and the character he played so authentically, Tony Soprano.
"I have gotten to know Jimmy and many of the otheractors in the Sopranos cast and I can say that each of them are an individualNew Jersey treasure.
"Mary Pat and I express our deepest sympathies to Mr Gandolfini's wife and children, and our prayers are with them at this terrible time."
Celebrities have been paying tribute to Sopranos star James Gandolfini, 51, who has died of a suspected heart attack whilst on holiday in Rome, Italy.