Thailand's 88-year-old king, the world's longest-reigning monarch, has undergone heart surgery, the Thai Royal Household Bureau said.
King Bhumibol Adulyadej has had a lengthy spell in hospital in Bangkok and has not been seen in public for months.
The king is widely revered and seen as an arbiter in the country's divided political arena.
Thailand is preparing to celebrate 70 years of his reign on Thursday.
The monarch was treated for narrowing of the arteries with "satisfactory results", the palace said in a statement.