By Stephen Gibbs
BBC News, Havana
The Venezuelan leader, Hugo Chavez, has ended a visit to Cuba expressing confidence that relations between the two countries are closer than ever.
The two leaders both displease the US
President Chavez said Cuba and Venezuela's cooperation were examples of what socialism can and should do.
US administration officials are concerned that both President Chavez and Fidel Castro are intent on undermining democracies in the region.
The two leaders emphatically reject the US charges.
Fidel Castro accompanied Hugo Chavez to Havana airport for a send-off which ended what Cuban media has been portraying as "a triumphant visit".
"The best ever," said President Chavez as he left.
The Venezuelan leader took the opportunity to brush aside recent comments from the US evangelist Pat Robertson, that he was a threat to the United States and should be assassinated.
Over the last three days, both Presidents Castro and Chavez have been showcasing their joint social projects and dismissing US charges that they are up to no good.
The statistics of their alliance are impressive.
Cuba currently sends a fifth of all its doctors to Venezuela.
This year alone 50,000 Venezuelans have come to Cuba to receive free eye treatment.
In return, oil-rich Venezuela sends Cuba 90,000 barrels of crude a day at highly preferential terms.
The deal has been forged by two leaders who do genuinely appear to be friends.
During a joint appearance on a six hour TV phone-in programme on Sunday, both presidents, dressed almost identically in military fatigues, joked together as they discussed their cooperation.
During the programme, Hugo Chavez made a point of saying that he didn't see Cuba's form of government as a dictatorship.
"It's a revolutionary democracy," he said.
President Chavez's next stop on his Caribbean tour is Jamaica.
There he is expected to sign a deal whereby Venezuela supplies oil to countries across the region under generous financial terms.
It is a deal which should go some way to shield Caribbean nations from rising oil prices.