MILAN (Reuters) - Silvio Berlusconi is expected to undergo surgery on Tuesday, his doctor said on Saturday, after the four-time Italian prime minister was admitted to hospital this week with a heart problem.

A spokeswoman for Milan's San Raffaele hospital, where the 79-year-old centre-right leader will have a defective aortic valve replaced, confirmed the comment made to reporters by Berlusconi's personal doctor Alberto Zangrillo.

The media mogul said in a message on Facebook on Friday his Forza Italia party was perfectly able to function despite his absence, ahead of a run-off vote in municipal elections on June 19.

(Reporting by Valentina Za; Editing by Dominic Evans)