The fall of the Soviet Union changed the relationship between the two nations. After the Soviet Union collapsed, trade between the Eastern Bloc nations and Cuba came to a grinding halt.
Putin tried to kick start it a few years ago--but he did so in order to mask discontent over the proposed missile defense system that was being built in Poland (when the Bush Administration was pushing the program).
Fidel tried to open up business opportunites several years ago when a host of companies such as Catepillar went to Cuba for a conference, but that endeavor went nowhere.
Since the collapse of the Soviet Union, Cuba has suffered greatly. In order to appease the masses, I'm sure Fidel has found ways to make his people happy. He's relaxed tourism, allowed the free exchange of American money (something that was STRICTLY forbidden beforehand)...and allowed some stores to sell American merchandise.