Prince Rainier III is suffering from cardiac and kidney failure and has been placed on a respirator, the palace said Wednesday.

An official medical update described the 81-year-old prince's condition as "stable" on the second day of his transfer into the intensive care unit of the Cardio-Thoracic Center.

Rainier, whose movie-star wife, Grace Kelly (search), died in a 1982 car crash, was hospitalized two weeks ago with a chest infection. After a marked improvement, the prince's health suddenly worsened.

A palace statement Wednesday said Rainier was transferred to the intensive care unit after developing a sudden respiratory infection "with cardiac and kidney insufficiency."

"Breathing difficulties made the installation of artificial respiration indispensable," the statement said.

Rainier has a history of heart problems and recently has been plagued with recurring problems linked to his respiratory tract. The prince has been hospitalized numerous times during the past decade.

Crown Prince Albert (search), 47 — his heir — traveled from abroad to visit his father, as did 48-year-old Princess Caroline (search), an official familiar with the situation said on condition of anonymity.

Princess Stephanie (search), 40, was seen entering and leaving the hospital.

Monaco, a tiny principality famous for its casinos, Formula One (search) Grand Prix and tax breaks that attract the rich and famous, is nestled on the Mediterranean Coast between Italy and the French Riviera.

Rainier assumed the throne in 1949. Monaco's constitution was revised in 2002 to allow the unmarried Albert to succeed his father despite his lack of heirs.

According to Article 10 of the constitution, Caroline would succeed Albert should he die. She, in turn, would be succeeded by her oldest son, Andrea Albert Pierre (search), 20.

Daily life in the principality went on as normal despite the news that its increasingly fragile ruler had suffered a setback. On Wednesday morning, Stephanie's three young children were seen going to school as usual.

"He has been a very good man and very good to us, the Monegasques," said Claudia Marino, 85, who says her family has lived here for four generations. "Yesterday, I received an Easter egg with his calling card, the tradition for years."