The break-up of the Soviet Union and the collapse of eastern European Communism hit no one harder than the long-time Cuban leader.
Communist Cuba, virtuallyblockaded by the United States and ostracised by most of the world, had for three decades relied almost exclusively on the Soviet bloc for political clout and economic survival.
Since the Soviet break-up and shift towards capitalism, the Caribbean island has been forced to fend for itself, the US has tightened the screws, and Mr Castro's one-party Marxist-Leninist regime has looked increasingly as though it is on its last legs.
A Russian Communist victory tomorrow could give Castro the political and economic oxygen he needs to keep his system alive and his personal authority intact.
Indeed, Castro needs a friend more than ever; in direct ratio totheir hunger - even the most basic foodstuffs they are supposed to receive on their rationing books are unavailable - Cubans are questioning his tenure. More Russian aid just might put some food on the shelves.
The Cuban leader maintained polite relations with Russia's current President. But as Boris Yeltsin opened up politically and economically, he had neither the time, money nor inclination to concentrate on the little island that, in the Kennedy-Khrushchev era, brought the world to the brink of war.
The Soviet troops have long gone, but their legacy is obvious in the number of young Cubans with names such as Vladimir or Tanya.
On the political and diplomatic front, a Communist Russia, as a member of the United Nations Security Council, would go a long way to easing Cuba's isolation.