The Australian newspaper said the 80-year-old prince was admitted Tuesday to a heart and chest clinic in the principality. Palace officials said Rainier expects to be home by next Thursday, Christmas Day.
The leader of Europe's longest-ruling royal family, the Grimaldis, Rainier underwent heart surgery in 1999. He had two operations in 2000 and was hospitalized during 2002 for fatigue and bronchitis.
Rainier was married to movie star Grace Kelly, who died in a 1982 automobile accident.
Monaco, smaller than New York's Central Park, was once a resort favored by European royalty. Now it is a tax haven popular with celebrities, financiers and sports figures.