The triple Emmy Award-winning star of "The Sopranos" died Wednesday while on vacation with his son Michael, who had just graduated eighth grade, TMZ said.
CBS News quoted Dr. Claudio Modini of the Policlinic Umberto I hospital as confirming Thursday the 51-year-old actor died of cardiac arrest.
The New York Post said Gandolfini suffered the heart attack in the bathroom of his hotel after a day of sightseeing with his 13-year-old son.
The boy alerted hotel staff after finding his father collapsed on the floor, the newspaper said.
CNN said an autopsy had to be performed and a death certificate issued before Gandolfini's body can be released and transported home for burial.