BANGKOK (AP) — Thailand’s elderly queen was hospitalized with a rapid heartbeat that returned to normal after a day of treatment, the palace said in a statement Saturday.

The brief statement by the Royal Household Bureau said 78-year-old Queen Sirikit, who is the wife of Thailand’s constitutional monarch, was admitted to a Bangkok hospital on Thursday but did not say when she was expected to check out.

"Her Majesty the Queen had a rapid heartbeat. The doctors therefore asked her to travel to and stay at Chulalongkorn Hospital on the night of Sept. 30," the statement said.

The statement said her "heart rate became normal on the night of October 1," but it was vague about what the treatment was.

Official statements about the royal family are traditionally formal and discreet.

The queen’s hospitalization was first reported Friday evening by the official Royal News and broadcast on all Thai TV stations. The initial report did not give any details of the queen’s medical condition.

The revered, ailing 82-year-old King Bhumibol Adulyadej visited his wife Friday on a rare trip away from a different Bangkok hospital where he has spent the past year.

An avid photographer, the king held a camera as aides wheeled him in to see his wife.

The king attended a concert held in his honor Wednesday at Siriraj Hospital, where he was admitted on Sept. 19, 2009, for what the palace described at the time as an inflammation of the lungs. The reason for his extended stay has not been explained.

Bhumibol, the world’s longest-serving monarch, has been king of Thailand for 64 years. Bhumibol has no formal political role, but he is regarded as the sole unifying figure in a politically polarized country.

The king’s health is an extremely sensitive topic in Thailand because of concerns that the succession may not go smoothly. The heir apparent, Crown Prince Vajiralongkorn, does not yet have the stature or moral authority of his father.

Open discussion of the matter — and all matters pertaining to the royal family — is barred by strict laws that make criticism of the monarchy punishable by up to 15 years in prison.

Associated Press Writer Thanyarat Doksone contributed to this report.