"El Comandante has fought a great battle, and, as he told us, he will overcome each of these moments little by little. He's getting better," Arreaza said.
Chavez also called for his supporters to vote in Venezuela's gubernatorial elections Sunday, Arreaza said.
"He is now completely in full intellectual conditions to send this message to the Venezuela," Arreaza added.
Maduro told Arreaza to give Chavez a message: "Tell him that the people here are on their feet working, battling." Maduro expressed confidence that Chavez's allies will win Sunday's elections.
Maduro also said National Assembly President Diosdado Cabello made a quick trip to Havana on Friday along with Attorney General Cilia Flores and they were in contact with Chavez's family.
"Praying together, we're going to achieve the miracle," Maduro said.
The vice president, whom Chavez recently designated his preferred successor, also repeated his government's condemnation of President Barack Obama's criticisms this week of "authoritarian policies" in Venezuela. Maduro called Obama's comments "unacceptable."
Saturday night's ceremony was held on the eighth anniversary of the creation of the leftist Bolivarian Alliance, or ALBA, bloc of nations, which includes Venezuela, Bolivia, Cuba and other nations.
Maduro read aloud a letter from Castro in which he said "the name of Hugo Chavez is admired and respected throughout the world." The former Cuban president was quoted as writing that "the doctors are fighting with optimism" for Chavez's recovery.
Bolivian President Evo Morales, who attended the event in Caracas, told the television network Telesur that he hadn't yet been able to travel to Cuba but that he hoped to meet with Chavez soon. He didn't give details.
Chavez's daughter Maria, who was with the president in Havana, thanked supporters for their prayers in a message on her Twitter account.
"We are continuing to battle along with papa," she said, expressing trust in "the hand of God!"
Associated Press writers Vivian Sequera and Ian James contributed to this report.