James Gandolfini's Son Witnessed Dad in Cardiac Arrest

June 20, 2013— -- "The Sopranos" actor James Gandolfini was at a Rome hotel vacationing with his son Wednesday when paramedics brought him to a hospital in cardiac arrest, officials said. Doctors pronounced him dead less than an hour later.

Gandolfini, 51, was in his room at Hotel Exedra when he became ill around 10 p.m. local time, officials said. His son Michael, 13, called the reception desk for help, Laura Conti, marketing director of the hotel chain told ABC News.

When hotel staffers arrived in Gandolfini's room, they immediately called for an ambulance, she said. Conti said the actor was alive when the ambulance left for Policlinico Umberto I hospital in central Rome.

Gandolfini arrived at the hospital at around 10:40 p.m. in cardiac arrest, Prof. Claudio Modini, director of the Emergency Department of the Policlinico, told ABC News. The paramedics in the ambulance had already started the resuscitation procedures. Those efforts continued after arrival at the hospital for 40 minutes, after which Gandolfini was declared dead, Modini said.

Learn More on the Life and Career of James Gandolfini

The cause of death is unknown and the autopsy will take place Friday, at least 24 hours after death occurred, as required by Italian law. It will determine whether the cardiac arrest resulted from a heart attack and whether there were any mitigating circumstances.

Gandolfini's body has since been transferred from the hospital to the Rome city morgue. After the autopsy, the U.S. Embassy will work with the morgue to bring Gandolfini's body back to the United States.

Gandolfini was expected to attend the Taormina Film Festival in Sicily this weekend and receive the "Taormina City Prize." Instead, organizers of the festival are scrambling to put together a tribute to the actor.

Organizers Mario Sesti and Tiziana Rocca told The Associated Press they had spoken to Gandolfini hours before his death, "and he was very happy to receive this prize and be able to travel to Italy."

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His managers, Mark Armstrong and Nancy Sanders, said, "It is with immense sorrow that we report our client James Gandolfini passed away today while on holiday in Rome, Italy. Our hearts are shattered and we will miss him deeply. He and his family were part of our family for many years and we are all grieving."

Although he rose to his greatest fame playing a New Jersey mob boss on "The Sopranos," Gandolfini also had a long and diverse list of credits as a stage and film actor, including many character and supporting roles.

"He was a genius. Anyone who saw him even in the smallest of his performances knows that," "Sopranos" creator David Chase said in a prepared statement this evening. "He is one of the greatest actors of this or any time. A great deal of that genius resided in those sad eyes.

"I remember telling him many times, 'You don't get it. You're like Mozart.' There would be silence at the other end of the phone. ... He wasn't easy sometimes. But he was my partner, he was my brother in ways I can't explain and never will be able to explain."

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After "The Sopranos" ended its run in 2007, Gandolfini received a Tony nomination starring in the Broadway hit, "God of Carnage," described in a 2009 New York Times article as a "satiric comedy."

Gandolfini is survived by his wife, Deborah Lin, his daughter Liliana, 8 months old, and his son, Michael, from a previous marriage.

ABC News' Anthony Castellano, Michael James and Lesley Messer contributed to this report.