MILAN — Doctors say former Premier Silvio Berlusconi is suffering a serious case of aortic insufficiency and will undergo surgery to replace the valve.

Berlusconi’s personal doctor, Alberto Zangrillo, told reporters Thursday that the 79-year-old billionaire businessman will be “better than before” after the four-hour surgery, which will take place before the middle of next week.

Berlusconi, who has a pacemaker, reported heart irregularities Sunday from Rome and Zangrillo advised him to return to Milan to be checked.

Zangrillo said a team of doctors at Milan’s San Raffaele clinic ran a battery of tests and diagnosed a serious case of aortic insufficiency, which happens when the aortic valve of the heart leaks, causing blood to flow in the reverse direction.