But Chavez anointed Maduro for that role, and the vice president has assumed the mantle even as the government has named him as the ruling socialist party's candidate in the presidential vote.
The military also appears to be showing firm support for Maduro despite a constitutional mandate that it play no role in politics.
In a tweet late Tuesday, state television said the defense minister, Adm. Diego Molero, had pledged military support for Maduro's candidacy against likely opposition candidate Henrique Capriles, raising concern among critics about the fairness of the vote.
Capriles, the 40-year-old governor of Miranda state who lost to Chavez in October, was conciliatory in a televised address after the president's death.
"This is not the moment to highlight what separates us," Capriles said. "This is not the hour for differences; it is the hour for union, it is the hour for peace."
Other opposition leaders were more critical of the military stance.
"When all Venezuela wants unity and peace, and a climate of respect between Venezuelans predominates, they're contrasted by what's unacceptable, the declarations of the minister of defense, that are, besides false, unconstitutional," said Ramon Guillermo Aveledo, executive secretary of the opposition coalition.
