President Boris Yeltsin's heart operation, now likely to take place next week, is shaping up not only as a test of his own physical powers but of the strength of Russia's constitutional order.
Can Russia's fledgling political institutions, most of them less than 3 years old, take the strain when the president, the apex of the new constitutional system, disappears under the surgeon's knife and undergoes a lengthy convalescence?There are historical precedents aplenty for incapacitated Kremlin leaders who ruled over Russia in name only while real power was exercised by others.
But the rules of the game have changed in Russia since the days of the Soviet Union, when political stability was unaffected by the ailments of a series of sick leaders. Now the stakes are higher.
Leonid Brezhnev, Communist Party leader from 1964 to 1982, presided over a period of calm and predictability in the Soviet Union. But from the mid-1970s he was medically unfit to govern, addicted to drugs and only able to concentrate for short spells.
His successor Yuri Andropov spent most of his brief term in power in hospital with kidney failure. When he died in 1984 his replacement was another invalid, the wheezing emphysema sufferer Konstantin Chernenko.
Paradoxically it was the vigorous and healthy Mikhail Gor-ba-chev, who took over in 1985, who destabilised the political system by trying to push through democratic reforms. Within a little over five years, it had collapsed.
Some historians, looking to medieval Muscovy, say Russia was always at its most stable when the nominal leader was a weak or incapacitated figurehead - Brezhnev being the best example.
The theory says real power in Russia has mostly been wielded by bureaucrats reporting to a Soviet-style "collective leadership" rather than by autocrats, whose challenges to the status quo have mostly plunged the country into chaos.
However the factors that kept the Kremlin power system running smoothly in Soviet times - including centralisation and tight secrecy - are less effective today.
Much has changed in Russia's political system since the collapse of communism, at the hands of Yeltsin himself. His 1993 made-to-measure constitution turned the head of state into the key figure in the political system.
Instead of a centralised system with all power flowing down from the Communist Party Politburo, Russia now has a basic law that lays down respective powers of the presidency, the two chambers of parliament, the government and the courts.
But the rules of the game are vague and imprecise, and without a healthy president in charge, the balance is easily upset, and political infighting could get out of hand.
When Brezhnev, Andropov or Chernenko were in the hospital, the old system functioned like clockwork; Politburo meetings went ahead normally, and the party's second secretary took the chair.
But until Yeltsin hands over all his powers temporarily to Prime Minister Viktor Chernomyrdin, nobody can formally deputize for him in this way or sign decrees in his name.