Czech President Milos Zeman has been taken to hospital amid political upheaval after a surprise opposition win in parliamentary elections.
The 77-year-old is a heavy smoker and former heavy drinker who uses a wheelchair and suffers from diabetes.
He was due to lead talks on forming a new government after Saturday's vote.
Prague's Central Military Hospital director said Mr Zeman was in intensive care for complications from a known condition.
"We know the diagnosis precisely, which allows us to target treatment," director Miroslav Zavoral said, but added that he would not give any further details per the president's request.
Mr Zeman's office has previously said he is suffering from exhaustion and dehydration, after spending eight days in hospital last month.
The president was taken to hospital from the presidential chateau outside the capital Prague on Sunday morning, shortly after a meeting with Prime Minister Andrej Babis.
Footage broadcast by Czech media show staff holding up his head as he entered the hospital.
Source: BBC News