Alberto Zangrillo said he saw Berlusconi on Monday and decided to transfer him to Monaco’s Cardiothoracic Centre because he deemed it “imprudent” to bring him to Italy, which is 15 kilometres from the small city-state.
Italian news agency ANSA first reported the news.
It was not immediately clear if the health emergency had been overcome.
“I would like to reassure everyone: I am in good health, my hospitalisation was necessary only for some more than routine tests imposed by the prudence of my doctors,” Berlusconi later wrote on his Facebook page.
“My activity continues normally, in constant contact with my collaborators and the protagonists of public life, in this very difficult moment for the country.”
The 84-year-old media tycoon underwent major heart surgery in 2016 and has also survived prostate cancer.
Last September he was hospitalised after contracting coronavirus.
He later told reporters that the virus had posed “the most dangerous challenge” of his life.
Berlusconi remains the leader of the opposition Forza Italia (FI) party.
Italy is currently in the grips of a political crisis that could potentially topple Prime Minister Giuseppe Conte.
Newspapers have speculated that some FI lawmakers might agree to help prop up the administration to prevent early elections.
