The hospital says Mr Havel had complications after surgery
The former Czech President Vaclav Havel is in a serious but stable condition after undergoing surgery at a hospital in Prague.
An aide to Mr Havel, Sabina Tancevova, said he was being treated for an unspecified inflammatory disease.
He is expected to remain in hospital for a few more days.
The 72-year-old hero of the 1989 Velvet Revolution has had health problems for many years. He steered Czechs to democracy after the fall of communism.
A hospital spokeswoman, Eva Jurinova, said Mr Havel had had an operation on his throat.
"He is doing breathing exercises. We can't offer a prognosis now, further steps will be decided tomorrow," she said.
A history of problems
Mr Havel has a history of respiratory problems dating back to his years in communist jails.
He has been plagued by chronic bronchitis since a third of his right lung was removed in December 1996 following the discovery of a cancerous tumour, the AP news agency reports.
Last year he was admitted to hospital suffering from acute bronchitis complicated with heart arrhythmia.
In 1998, he was rushed to hospital with a ruptured colon, and there was widespread concern at the time that he might not survive the surgery.
The former chain smoker has also suffered repeated heart problems.
Vaclav Havel was a dissident playwright when he led the 1989 revolution that ousted the Soviet-backed communist regime without bloodshed, after four decades of authoritarian rule.
He was elected Czechoslovakia's first post-communist president in 1989 and then became president of the Czech Republic formed in 1993.
His last term in office ended in 2003.