The last time anyone filmed a fact-based story of Czech war heroes the Czech Republic was still part of Czechoslovakia and the East bloc was still under Soviet occupation.

This week Czech audiences at the Karlovy Vary fest fought to hold back tears as they watched Sean Ellis’ portrait of a Czech and a Slovak who pulled off the highest-level Nazi assassination of World War II.

Just why no Czech producer has been willing to tackle the story of how British-trained Czechoslovak paratroopers Jan Kubis and Jozef Gabcik took down Reichsprotekor Reinhard Heydrich in 1942, no one can say.

But Czech producer David Ondricek, who worked with French and American producers to complete the “Anthropoid,” Sean Ellis’s moving story of that killing and its aftermath, says the project gained strength from being an international production — just as the secret mission was.

And this time around, the historical accuracy and involvement of Czech experts is a league apart from the 1975 film on the event, “Operation Daybreak.” Ellis, who obsessively researched “Anthropoid” for 15 years before writing the script, developed his characters using scraps of historic documentation, working closely with Czech military archives and eye-witness accounts.

The accuracy of the film extended to an exact copy of the Baroque Church of Saints Cyril and Methodius in Prague where the two assassins, along with five other members of the resistance, where finally discovered by the Nazis, leading to an hours-long fire fight before the Czech and Slovak fighters finally shot themselves rather than surrender.

“I really admire them,” says Czech actress Anna Geislerova, who plays a Prague woman whose efforts to help Kubis and Gabcik cost her her life. “They chose a side. They didn’t choose to wait and see.”

Her character, one of the few in the film that is a composite of experiences of Praguers living under Nazi occupation, touched her deeply, Geislerova admits. “She was strong enough to risk everything,” the actress says.

The church set, which barely fit into the capacious soundstages of Barrandov Studio, served as highly symbolic backdrop to the film’s climax, which escalates using authentic attack and resistance strategies, weapons and characters.

Ellis says it was critical to him to shoot the story in Prague, with Czech actors, using authentic locations wherever possible. Thus, leads Jamie Dornan and Cillian Murphy had to adopt the accents Czechs use when speaking English — often with Geislerova as coach.

Audiences in Karlovy Vary clearly were touched by the tribute, which scored among the top audience faves at the festival. With “Anthropoid” sold in the US and UK so far, producers are now keen to see how the powerful story of sacrifice touches hearts in those territories and beyond.

Ellis says the film forces viewers to confront a difficult question: “What’s the human psyche and what’s it capable of doing at extreme points? You kind of know there’s no way out and it’s the end — it’s kind of how you face the end.”

The director says Kubis and Gabcik handle the consequences of their act, for which 5,000 Czechs were killed in retribution by the Nazis, with honor. “In ‘Anthropoid’ they face the end with such a roar of life that it’s still resonating today.”