Legislators will choose a president, two vice presidents and other leaders of the National Assembly, which is controlled by a pro-Chavez majority. Whoever is elected National Assembly president could eventually end up being the interim president of Venezuela under some circumstances.
Brewing disagreements over how to handle a possible transition of power could also be aired at the session.
"If the opposition thinks it will find a space in the National Assembly to conspire against the people, it's mistaken once again. It will be defeated," National Assembly President Diosdado Cabello said in a message on Twitter, saying the legislature will stand with Chavez.
The government revealed this week that Chavez is fighting a severe lung infection and receiving treatment for "respiratory deficiency" more than three weeks after undergoing cancer surgery in Cuba.
Chavez hasn't spoken publicly or been seen since his Dec. 11 operation in Cuba, and the latest announcement suggests a deepening crisis for the 58-year-old president.
But Maduro criticized rumors surrounding Chavez's condition, saying: "He has a right to his privacy, and to recover."
The government's account of Chavez's complications raised the possibility that he might be breathing with the assistance of a machine. But the government did not address that question and didn't give details of the president's treatment.
Independent medical experts consulted by The Associated Press said the government's account indicated a potentially dangerous turn in Chavez's condition, but said it's unclear whether he is attached to a ventilator.
Dr. Gustavo Medrano, a lung specialist at the Centro Medico hospital in Caracas, said he has seen similar cases in cancer patients who have undergone surgery, and "in general it's very bad, above all after a surgery like the one they performed on him."
"I don't know the magnitude of the infection he has, how much of his lungs have been compromised, how much other organs are being affected. That's not clear," Medrano said.
"What's most likely is that he's on mechanical ventilation," Medrano added. However, he said, while respiratory deficiency means there is an abnormally low concentration of oxygen in the blood, depending on the severity it can be treated in various ways.
Dr. Michael Pishvaian, an oncologist at Georgetown University's Lombardi Cancer Center in Washington, agreed that such respiratory infections can run the gamut from "a mild infection requiring antibiotics and supplemental oxygen to life-threatening respiratory complications."
"It could be a very ominous sign," Pishvaian said. He said it's possible Chavez could be on "life support," but added it's impossible to be sure without more details.
Opposition leaders have blamed vague information coming from the government for persistent rumors about Chavez's condition, and demanded a full medical report.
Chavez has undergone four cancer-related surgeries since June 2011 for an undisclosed type of pelvic cancer. He also has undergone chemotherapy and radiation treatment.
He was re-elected in October to another six-year term, and two months later announced that the cancer had returned. Chavez said before the operation that if his illness prevented him from remaining president, Maduro should be his party's candidate to replace him in a new election.
The Venezuelan newspaper El Nacional criticized what it called an "information vacuum" in an editorial on Friday, saying Venezuelans are in the dark because "no one speaks clearly from the government." The newspaper called the situation reminiscent of secrecy that surrounded the deaths of Josef Stalin in the former Soviet Union and Mao Zedong in China.
State television repeatedly played video of a song in which rappers encourage Venezuelans to pray, saying of Chavez: "You will live and triumph." A recording of a speech by Chavez appears during the song, saying: "I will be with you always!"
AP Interactive: http://hosted.ap.org/interactives/2012/venezuela/
Ian James on Twitter: http://twitter.com/ianjamesap