End of Chávismo spells woe for Castros Havana is full of whispers. Cuban officials trade on rumours of the great man's health. Reports that the treatments are taking effect are dashed by new ones that his days are numbered. For some, his heartbeat is almost synonymous with their revolution. How long can the regime last without him at the helm? Of course, the object of their concern isn't Fidel Castro - it's Hugo Chávez. Although the Americas" leading leftists are ailing, the Venezuelan president's death would be far more costly for the Cuban government than Mr Castro's own passing. Yes, the "Maximum Leader" and regime founder can never truly be replaced, but the tropical dictatorship has long prepared for that inevitability, passing all real duties to his younger brother Raúl more than seven years ago. But as the reports from Caracas become more grim - Venezuelan officials gave a bleak bulletin on Mr Chávez's health on Monday - Havana is steeling itself for a post-Chávez world. Because officials there know the support that Cuba receives from the South American sultan is the lifeline that keeps the regime afloat. First, there is the oil: more than 100,000 barrels a day provided at cut-rate prices. Indeed, Mr Chávez's largesse for Cuba has been so great, it has outstripped the island's own needs. The Castro government is believed to resell as much as 40 per cent of the oil Venezuela provides. Yoani Sánchez, Cuba's leading dissident and blogger, has dubbed the Venezuelan oil supply "Cuba's Viagra." Then there are hundreds of co-operation projects, joint ventures, shipping and port renovations, and enormous sums of direct investment. Fidel Castro has valued the relationship for Cuba at about $7bn a year. Indeed, cementing his ties to Venezuela's strongman - beginning with their first meeting in 1994 - was Mr Castro's final masterstroke for buttressing his regime after the collapse of the Soviet Union. But Mr Chávez's death will have greater economic and political ripples across several authoritarian regimes. A clutch of regional states - Bolivia, Ecuador and Nicaragua - will lose their most important ally and loudest spokesman. Russia will lose one of its largest arms buyers. Iran will no longer have a key partner for its anti-American diplomatic gambits. China will not have trouble purchasing Venezuelan oil, but its hopes for preferential access may be questioned with Mr Chávez no longer on the scene. After all, Mr Chávez's electoral success, particularly his victory in October 2012, was won in part with generous assistance - often in the form of discount washing machines and microwaves to hand out at campaign rallies - from Beijing. Few Venezuelans will miss the Comandante's foreign policy. They voted for him because of his domestic initiatives and for keeping the oil tap on for one populist project after another. Most Venezuelans, even a fair number of Chávistas, greeted their president's foreign agenda with an eye roll. The logic for why Venezuela should have close relations with Belarus or some other distant central Asian regime usually escaped them. I was present when the Venezuelan National Assembly voted to open diplomatic relations with South Ossetia in 2010. By doing so, Venezuela joined Russia, Nicaragua and Nauru as the fourth state to establish formal channels with the region that had broken away from Georgia two years earlier. I pressed several legislators from Mr Chávez's ruling party on the nature of Venezuela's interests in the region that had broken away from Georgia. What projects might they embark on? What initiatives might they advance? My questions were met with blank stares. Of course, the most obvious explanation was to court good will with Moscow. But nowhere are the stakes for what follows Mr Chávez greater than in Cuba. The ties between the two governments are so deep that Mr Chávez sometimes described the two countries as if they were a single entity: "Venecuba." And it is an apt description: more than 5,000 Cuban military and political advisers are believed to be serving in the Venezuelan government and armed forces. Mr Chávez's government has leaned heavily on Cuba's intelligence service, G2, for everything from keeping tabs on its political opponents to helping ensure the president's safety. Indeed, Mr Chávez's designated successor, Nicolás Maduro, is a Castro-approved leftist who has deep sympathies for the Cuban revolution. All of these bonds are Cuba's last hedge for maintaining relations with Venezuela, and a President Maduro would not be lacking for Cuban advice given the deep footprint Mr Castro's advisers have in Caracas. Nevertheless, Havana knows that there is only one Hugo Chávez, and as Chávismo crumbles so goes the last best hope for a Cuban experiment that failed long ago. The writer is the politics and foreign affairs editor at Slate magazine and author of "The Dictator's Learning Curve: Inside the Global Battle for Democracy"