King Bhumibol Adulyadej, the world's longest-reigning monarch, has been treated for various ailments during a year-long hospitalization in the Thai capital.
He was last seen in public on January 11, when he spent several hours visiting his Bangkok palace.
The king's heartbeat, breathing and blood pressure were normal, the palace said, adding that an electrocardiogram showed an increased supply of blood to the heart.
The king, who celebrated 70 years of his reign on Thursday, is seen as a unifying figure in a country that has faced decades of often deadly political upheaval.
On a few occasions the monarch has intervened when events threatened to plunge the country into crisis.
In a June 7 statement, the palace said the king had received treatment for narrowing of the heart arteries with "satisfactory results".
News about the royal family is tightly controlled in Thailand. Laws protecting the royals from insult make it a crime to defame, insult or threaten the king, queen, heir to the throne or regent.
Editor: Ade P Marboen
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