Interviews with voters in rich and poor neighborhoods of Caracas, the capital, indicated many past supporters of Chavez and his party were eager for a change.
"Twenty years ago, there were no lines. Now we have to wait to get anything at drugstores and markets. Even so I can't find tires, batteries and motor oil that I need for my work. And the money I make isn't enough," said Teodoro Mendez, a 62-year-old taxi driver and former Chavez supporter who said Sunday that he voted for a MUD candidate.
Others said they were voting for opposition candidates to protest Venezuela's rising crime rate. Accountant Maria Gabriela Montilla, 37, who recently had been robbed twice said, "A change is necessary."
"We need diversity in the government, not just one powerful party," she said after voting in Caracas' low-income Prado de Maria district.
This year has been the worst for Venezuela's economy since the so-called Caracazo riots of 1989 and especially hard for Venezuelans earning minimum wage who have seen their paychecks plunge 34% in inflation-adjusted terms, said Francisco Monaldi, an economist at Rice University in Houston.
Monaldi said Venezuela is so cash-strapped that it is at risk of defaulting on its $113 billion in foreign debt next year unless there is a rise in the price of oil, revenue from which the government derives 90% of its budget. As the government seeks to cope, consumers are faced with triple-digit inflation.
"Things will get worse before they get better," Monaldi said.
After voting in southwest Caracas, Henrique Capriles, the opposition governor of Miranda state who lost to Maduro in the election to succeed Chavez in April 2013, said the cratering economy and declining incomes favored opposition candidates.
"The only people who should be concerned are those in leadership who are going to lose their privileges," Capriles told reporters. "Who can defend a government when the poverty is rising at this rate?"
Addressing reporters after voting in west Caracas, Maduro said Venezuela has been victim of an "economic war" and defended the socialist revolution begun by Chavez, saying it was an "anchor of stability in the region."
Worsening conditions have driven many Venezuelans to migrate. Attorney Maria Trina Burgos, who now lives in Doral near Miami, said she came back to vote to defeat the "dictatorship."
"We want to clean everything up. Everyone out!" said Burgos after voting in the affluent Santa Rosa de Lima barrio of Caracas. An immigration attorney, Burgos said she represents several of the thousands of Venezuelans she says have applied for political asylum in Florida this year.
The political clout of an opposition-controlled assembly will depend on how big a majority the MUD won. If it took two-thirds or more of the 167 seats, the alliance would have the power to censure ministers, name supreme court judges and also promote a recall vote on Maduro's presidency early next year.
But even an overwhelming advantage at the polls may not translate into a proportional edge in representation. Chavismo, the socialist movement named for Chavez, traditionally has been stronger in rural areas, which are overrepresented in the assembly, said Luis Salamanca, a professor at Central University of Venezuela.
Still, he and other analysts saw little chance of Maduro's PSUV maintaining control of the congress.
"The polls and direct observation show that a majority of the population is [having] difficulties [because of] the scarcity, high cost and long lines for food," Salamanca said. "That irritates voters and gives those responsible for that irritation little basis to say, 'Vote for me again.'"
Schoolteacher Esperanza Figueira, 52, said she rarely votes but was moved to cast a ballot Sunday for an opposition assembly candidate to protest the failing economy.
"I am outraged that my salary isn't enough to even buy a pair of shoes," Figueira said. She described Maduro as "a wolf in sheep's clothing who talks to us as if we're ignorant and don't know what's going on."
Mendez, the taxi driver, agreed with that assessment, saying President Maduro is in over his head.
"The government does many positive things but many negative things as well," Mendez said after voting at a school in the poor Santa Rosalia district of west Caracas. "I don't think the people in charge are capable of doing their jobs."
Mogollon is a special correspondent.