Cuba has a faltering economy, with few little to offer potential trading partners in terms of big buck goods. It also has a surplus of military equipment, left over from the heyday of the Cold War, when the Soviet Union was extremely generous. The world market for military equipment is very lucrative, but Russia also has plenty of surplus equipment, and there's not been much of a market for Cuba's leftovers. Until recently.
Radical president Hugo Chavez of Venezuela has apparently become Cuba's best customer for military equipment. The two countries have already concluded several transactions, for naval and ground equipment, and more deals seem likely. In addition to being able to supply equipment, the Cubans are also able to provide maintenance, repairs, and modifications, and training. While Chavez could probably get the same deal - or even a better deal - from Russia, there are advantages to dealing with the Cubans. For one thing, there's no language barrier. In addition, the deals strengthen Chavez's ties to his good friend Fidel Castro, which promotes his prestige among revolutionary elites in Latin America.