His barbs added to weeks of insults in the run-up to the April 14 presidential elections triggered by the death of socialist leader Hugo Chavez this month. Polls show Maduro with a double-digit lead over opposition rival Henrique Capriles.
"The campaign against Cuba is just like the campaign against the Jews in Hitler's Germany," Maduro said during a rally in Chavez's home state of Barinas. "The heirs of Hitler are leading a campaign in Venezuela against the people of Cuba."
Chavez, ten years ago, began bringing Cuban doctors to Venezuela to provide free health care in slums and rural villages, and maintained close ties with the communist-run island's leadership throughout his 14 years in office.
Opposition critics say Maduro and other senior government figures are receiving guidance directly from Cuban President Raul Castro, as well as allowing Cuban advisers to wield influence in Venezuela's military and intelligence services.
Some extremists have called the Cuban doctors part of a plan to turn Venezuela into a Communist state, though nearly all opposition leaders say the program is positive and vow to maintain it.
Maduro is benefiting from an outpouring of emotion after Chavez' death and as well from the legacy of Chavez's wildly popular social welfare campaigns known as "missions" that include the Cuban doctors program.
Government sympathizers have at times used terms such as "Nazi" and "fascist" to describe Capriles, a descendant of Polish Jews on his mother's side.