ROME - Italy’s controversial former prime minister Silvio Berlusconi was undergoing cardiac surgery on Tuesday after a heart attack his doctor said could have killed the 79-year-old tycoon.

“At 8:00am (0600 GMT) this morning, the operation to replace his aortic valve began,” the San Raffaele hospital in Milan said in a statement.

The surgery is expected to last for four hours and Berlusconi will be in intensive care for another two days, the hospital said. The flamboyant media mogul and football club owner, who dominated Italian politics for nearly two decades, is expected to remain in hospital for several weeks.

Berlusconi’s 30-year-old companion Francesca Pascale was seen at the window of his hospital room, clutching a handkerchief. Italian media reports said his children were also at San Raffaele hospital.

The operation is being 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” parties, was admitted for tests at the hospital on June 7 after suffering a heart attack.

“He arrived at the hospital in a severe state, he risked his life, he risked dying and he knew it,” Berlusconi’s doctor Alberto Zangrillo told a news conference last Thursday.

He said the fault in the valve was “severe” and 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 tycoon, who has largely dropped off the political radar in Italy, was facing the operation “with great courage and determination”, he added.

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.

The device was replaced at the end of last year. “Naturally, I am concerned,” Berlusconi wrote on his Facebook page on Monday. “But I am also very moved by the very many demonstrations of appreciation, support and affection which I have received from everywhere, even from political rivals.”

Italy’s centre-left Prime Minister Matteo Renzi wished his rival “good luck”. Matteo Salvini, the head of the populist Northern League - a sometime ally but also rival on the rightwing of Italian politics - sent Berlusconi “best wishes for his quick return to the field”.