Russia's former nuclear energy minister Yevgeny Adamov has suffered a heart attack while in custody.
Yevgeny Adamov has denied the charges against him
Mr Adamov has been held at a detention centre in Moscow since his extradition from Switzerland to face fraud charges.
Officials say he fell ill at around 0500 (0100 GMT) on Thursday and was given medical assistance.
His lawyer told RIA Novosti news agency that this was Mr Adamov's third heart attack. A court has rejected calls for him to be released on health grounds.
A representative of the Federal Service for Execution of Sentences said his life was not in danger after the most recent attack.
Mr Adamov was formally charged after being extradited from Switzerland in December.
He was also wanted in the US on embezzlement charges. The US accuses Mr Adamov of embezzling up to $9m (£5.2m) it gave to improve security at Russian nuclear facilities.