Last week Maduro said Chavez was "in battle" and undergoing "extremely complex and hard" treatments, but he did not detail what the treatments involved. Government ministers have repeatedly said in recent weeks that the president's condition is improving.

Chavez has been battling cancer since June 2011, but officials have never revealed what type of cancer he has, and speculation has swirled about his health and political future. Venezuela's opposition has criticized the government's lack of transparency, while the government has accused political opponents and the media of spreading rumors about the president's health.

Vice president plays a prominent role

Meanwhile, on the Venezuelan political stage, Maduro has been front and center during El Comandante's absence. Maduro has spoken at political rallies around the country and delivered updates about Chavez on national television.

Last month, he told throngs of supporters that opponents were plotting to murder him.

Opposition critics have said he's campaigning for office -- a claim the government has denied. Maduro and other government officials have accused the opposition of printing fake campaign posters with Maduro's picture.

Before he left for Cuba for surgery last month, Chavez said he wanted Maduro to assume the presidency if he became incapacitated and called on voters to support Maduro at the polls.