Pavel Borodin, a former Kremlin aide awaiting extradition to Switzerland on money-laundering charges, has been taken back to prison, after being rushed to hospital on Tuesday following a suspected heart attack.
Borodin returned to his New York prison cell on Wednesday, after staging a complete recovery.
There had been conflicting reports about the severity of his condition. A statement from his office said he had suffered a coronary heart attack, but unidentified sources suggested his health was "more or less normal".
Borodin has been in a New York jail since January 17 following his arrest on a Swiss warrant. He is reported to have complained of heart pains on Sunday. He said the pains had been brought on by the stress of being arrested and imprisoned.
Swiss officials say they have evidence that Borodin had access to Swiss bank accounts containing about $25 million (SFr42 million) and that the money has now disappeared.
They suspect that Borodin received the money in kickbacks from two Swiss-based firms - Mabetex and Mercata - in return for lucrative contracts to renovate the Kremlin.
Russian prosecutors closed their investigation into the case last year, citing lack of evidence.
swissinfo with agencies