CARACAS, Venezuela (AP) -- Venezuelan President Hugo Chavez was heading back to Cuba on Sunday for a third cancer surgery after naming his vice president as his choice to lead the country if the illness cuts short his presidency.
Chavez's announcement on Saturday night unleashed new uncertainty about the country's future, and his supporters poured into city plazas across the nation to pray for his recovery from what appears to be an aggressive type of cancer.
Some wiped tears, while others held photos of him and chanted in unison: "Ooh-Ah! Chavez isn't going away!"
Chavez acknowledged the seriousness of his health situation in a televised address, saying for the first time that if he suffers complications Vice President Nicolas Maduro should be elected as Venezuela's leader to continue his socialist movement.
Several outside medical experts said that based on Chavez's account of his condition and his treatment so far, they doubt the cancer can be cured.
Chavez said he hasn't given up.
"With the grace of God, we'll come out victorious," said Chavez, who held up a crucifix and kissed it during his Saturday night appearance.
The 58-year-old president is still scheduled to be sworn in for a new six-year term Jan. 10. He has been in office for nearly 14 years, since 1999.
"There are risks. Who can deny it?" Chavez said, seated at the presidential palace beside Maduro and other aides. "In any circumstance, we should guarantee the advance of the Bolivarian Revolution."
Chavez, who won re-election on Oct. 7, said he would undergo surgery in Havana in the coming days. Lawmakers on Sunday voted unanimously to grant him permission to leave the country for the operation.
During the session at the National Assembly, opposition lawmakers agreed to Chavez's request and also said that Maduro should take on his duties during his temporary absence, as the constitution specifies. Opposition lawmaker Julio Borges criticized the incomplete information that has been released about Chavez's cancer, saying: "Venezuela has a right to know the truth."
Throughout his treatment, Chavez has kept secret various details about his illness, including the precise location of the tumors and the type of cancer. He has said he travels to Cuba for treatment because his cancer was diagnosed by doctors there.
National Assembly President Diosdado Cabello said there are no plans at this time for Chavez to cede power, even temporarily, as president.
"He's not asking for permission to leave his duties," Cabello said. "The chief of this revolution is Hugo Chavez."
Cabello chided opposition politicians for questioning how forthcoming Chavez has been about his illness, likening them to "Komodo dragons."
Some of the pro-Chavez lawmakers cried and their voices cracked with emotion as they praised him and wished him a full recovery. They chanted, "Onward, commander!"
Under the Venezuelan constitution, as vice president Maduro would automatically fill in as president on a temporary basis should Chavez be unable to finish the current term concluding in early January.
But the constitution also says that if a president-elect dies before taking office, a new election should be held within 30 days. In the meantime, the president of the National Assembly is to be in charge of the government.
More than 1,000 of Chavez's supporters gathered on Sunday in Plaza Bolivar in Caracas to show solidarity, many wearing his movement's red T-shirts while a marching band played.
The president, who had just returned from Cuba early Friday, said on television Saturday that tests had found a return of "some malignant cells" in the same area where tumors were previously removed.
Chavez's quick trip home appeared aimed at sending a clear directive to his inner circle that Maduro is his chosen successor. He also called for his allies to pull together and said it's important for the military to remain united, too.
"The enemies of the country don't rest," he said, without elaborating.
Chavez said his doctors had recommended he have the surgery right away, but that he had told them he wanted to return to Venezuela first.
"What I came for was this," he said, seated below a portrait of independence hero Simon Bolivar, the inspiration of his Bolivarian Revolution movement.
Chavez had named Maduro, his longtime foreign minister, as his choice for vice president three days after winning re-election. The 50-year-old Maduro, a burly former bus driver, has shown unflagging loyalty and become a leading spokesman for the socialist leader.
Chavez said that if new elections are eventually held, his movement's candidate should be Maduro.