King Bhumibol Adulyadej of Thailand, the world’s longest-reigning living monarch, celebrates 70 years since ascending to the throne.
The celebrations began with a religious ceremony in the capital Bangkok, led by 770 Buddhist monks, an auspicious number.
King Bhumibol, 88, is revered by Thais, for whom he has been a figure of stability through the country’s decades of political upheaval.
However, the monarch is in poor health and has not been seen in public for months.
The procedure, known as balloon surgery, was to widen his arteries after tests showed the king had insufficient blood in the heart muscles, the statement said.
King Bhumibol has spent much of the past few years in hospital, and his health is closely watched by Thais.
“The relationship between Thais and the King is deep, more than one can actually begin to explain,” Col. Winthai Suvaree, a spokesman for the royalist junta, said to Reuters.
“He is a father to the land.”
Several hundred people had gathered outside the palace on June 9 to wish the king well.
The king is not expected to make a public appearance.
King Bhumibol’s popularity stems partly from his long reign and service to Thai people, but also because he is seen as an arbiter in politics.
Thailand has been wracked by political strife in recent years and is currently governed by a military-led government.
Strict lese majeste laws ban any criticism of the king or the royal family.