First indications were that the four-hour open-heart operation to replace his aortic vale at the San Raffaele hospital in Milan had been successful.
"The operation was finished a little after midday and there were no complications in the operating theatre," a hospital statement said, adding that Berlusconi had been transferred to an intensive care unit.
"Everything is okay guys, now I can speak more calmly," Gianni Letta, a close political ally of the billionaire leader of Forza Italia, told the AGI news agency.
Berlusconi's 30-year-old companion, Francesca Pascale, was seen at the window of his hospital room shortly after the surgery began, looking tearful and clutching a handkerchief.
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Italian media reports said the twice-divorced Berlusconi's five children were also at San Raffaele hospital.
The operation was conducted by Ottavio Alfieri, the head of the hospital's cardiac surgery unit.
The ageing billionaire, notorious for his brushes with the law and his "bunga bunga" sex parties, was admitted for tests at the hospital on June 7 after suffering a heart attack.
He said the fault in the valve was "severe" and that without the operation, "the risk of him dying within the year would be 10 percent".
But Zangrillo said he expected Berlusconi to be back to full health within a month, adding that successful surgery would leave him "better than before".
The one-time cruise ship singer turned centre-right politician suffered a heart attack 10 years ago and had a pacemaker fitted in the United States.
"Naturally, I am concerned," Berlusconi, who has largely dropped off the political radar in Italy, wrote on his Facebook page yesterday.