Orient claimed a 2-1 triumph at Swansea on Saturday to reach the last 16 while the Gunners saw off Huddersfield by the same scoreline on Sunday.
Hearn said: "We're in danger of breaking even - I don't what's happening these days with football! But the money is secondary. I've been chairman for nearly 16 years and we've never had anything like this. It's going to be a fabulous day out. I love the FA Cup."
Hearn insists the visit of Arsenal is more significant to him than a clash against neighbours West Ham would be.
He added on Sky Sports News: "We are two teams from the East End - we know each other too well. It's great to bring Arsenal down from north London - they're a massive team with world-class players.
"My team is full of characters and we're going to do our best to cause an upset. It's a massive game for our club. We've got a great manager (Russell Slade) and we'll hopefully give them a good game. It's come at the right time - we've only had two losses in our last 19 games. A little club like Leyton Orient need a reward every now and again. It's one of the reasons you support a small team."
Source: PA
Source: PA