The death of Venezuelan President Hugo Chavez is an especially tough blow for Cuba, whose feeble state-run economy has been propped up for more than a decade with Venezuelan oil shipments and other subsidies.
The Castro government has declared three days of mourning, calling Chavez "a son" of Cuba, but privately Cubans are quietly fretting about the potential loss of billions in trade and the threat of a new economic crisis.
When he was first diagnosed with cancer in 2011, Hugo Chavez turned to Fidel Castro and Cuba's doctors to save him. But his disease came back again and again, and when news of his death was announced by Cuba's state broadcasters Tuesday night, all of Havana seemed to go quiet.
Long before Chavez was first elected president in 1998, Castro saw him as a protégé. Havana sent doctors, teachers and military advisers to help Chavez consolidate power, and in turn, the Venezuelan president pulled Cuba out of the economic ditch left by the collapse of the Soviet Union.
The island came to depend on Venezuela for two-thirds of its oil imports and nearly half its foreign trade.
Among the tens of thousands of Cubans who went to work among Venezuela's poor was Alvaro Castellanos, a doctor standing on the sidewalk outside the Venezuelan Embassy in Havana, where he came to pay his respects.
"We gave them what we had, and in a way they gave us what they had," says Castellanos, adding that he spent six years working in Venezuela. "More than anything it was a family, a union, not just between Cuba and Venezuela but with all of Latin America."
Castellanos was among a handful of Cubans who arrived to the embassy, but Chavez's death brought no mass outpouring of emotion in Havana, unlike the scenes in Caracas.
Relationship Could Hinge On Election
The outcome of the Venezuelan presidential election in the next month will determine Chavez's successor and the future of relations with Cuba. A win by Chavez loyalist Nicolas Maduro would likely keep the oil flowing and the relationship tight.
But a victory by Venezuela's opposition could auger a new austerity period for Cuba. Eduardo Garcia, a university student in Havana, said he didn't think the Venezuelan people would vote for that.
"I have faith that this is a process that doesn't depend on a single person," he said. "I have faith that everything Chavez has done has taken root in the conscience of Venezuelans, and they will continue to follow his path."
To many in Venezuela and the U.S., Chavez was an autocrat who left his county divided and dysfunctional. But to many Cubans accustomed to harsher Castro rule, he looked a democratic figure, and helped push their rigid government in a better direction.
After all, Chavez based his rule on democratic elections. Compared to the Castros, he tolerated more criticism from opponents and the press. And even among frustrated Cubans who saw his aid as a lifeline to the Castros, they knew it was Chavez who kept the lights on and the air conditioners running.
Havana resident Miriam Suarez sees nothing good coming from his death.
"A lot of people who don't know what poverty is like can't understand Chavez," Suarez said. "Maybe now that he's gone there will be changes. And it'll be the poor who suffer, not the rich."
Tributes to Chavez and condolences have come from all over Latin America and the world since his death, but Fidel and Raul Castro have been noticeably silent.
The Cuban government issued a statement Tuesday night, but neither Castro has appeared in public nor offered a farewell statement.
For the elder Castro, now 86 and retired, Chavez's death is an especially personal loss. He has even outlived the man he carefully prepared to be his political heir.