The 86-year-old former president is being treated at the Meilahti Hospital in Helsinki.
Koivisto served as Finland’s president from 1982 to 1994 and as prime minister from 1968 to 1970 and 1979 to 1982. Following his last term as president, he has worked actively on writing his memoirs.
The Office of the President released the news about Koivisto's health.