The former head of Russia's anti-doping agency Rusada has died, the organisation says.
Nikita Kamaev's death comes two months after he resigned his post following a doping scandal in Russian athletics.
Rusada said the cause of death was "a massive heart attack".
Russia was suspended from international athletics last November. The World Anti-Doping Agency (Wada) accused Russian athletics of state-backed doping, corruption and extortion.
"He will remain in our memories as an experienced and understanding leader, distinguished by his high professionalism," the Rusada statement said, adding that Mr Kamaev, 52, was able to create a "friendly atmosphere" in his team.
His death comes just two weeks after that of Rusada founding chairman, Vyacheslav Sinev.
'Felt ill after skiing'
Russian Sports Minister Vitaly Mutko said: "It's a very unexpected death. [Mr Kamaev] seemed healthy and everything was fine."
Rusada's former director general, Ramil Khabriev, told the BBC: "I think he had a massive heart attack. His wife told me that he'd been cross-country skiing outside Moscow.
"He came home and felt ill and she called an ambulance. But when the ambulance came, they couldn't restart his heart. He died at his mother's country house.
"I never heard him complain about his heart... but those close to him say that he got tired after physical exercise and felt unwell.
"Of course the [doping] scandal affected him. He was distressed by it. He would send me links to reports on it every day. He followed what was published very closely."
Mr Sinev, who left the agency in 2010, died on 3 February.
But Mr Khabriev said there was no link as Mr Sinev had been ill for a long time with heart problems and was supposed to undergo a transplant.
Russia was provisionally suspended from international athletics, including the Olympic Games, in November by the International Association of Athletic Associations (IAAF).
The IAAF took action following the Wada report.
The suspension will remain in place until Russia convinces athletics authorities it has sufficiently changed its practices.
Along with Argentina, Ukraine, Bolivia, Andorra and Israel, Russia was deemed in breach of Wada codes.
Rusada was prohibited from carrying out any Wada-related anti-doping activity.
Mr Kamaev resigned from Rusada in December along with all the organisation's other top executives as Russia began work on lifting the ban in time for its athletes to compete at the Rio de Janeiro Olympics in August.