NEW YORK - In a sweltering midtown dance studio, two professionals from "Dancing With the Stars" were having the tables turned on them. On this recent afternoon, they were the dance students.

Karina Smirnoff and Maksim Chmerkovskiy were spinning each other around a mirrored room under the watchful eyes of a pair of Argentine tango pros - Victoria Galoto and Juan Paulo Horvath.

"No," Galoto said at one point, stopping the practice session and grabbing her partner to demonstrate to the TV stars how the steps are to be properly done. "Like this."

Smirnoff and Chmerkovskiy may be former Latin ballroom dancing champions and skilled enough each to be on 13 seasons of "Dancing With the Stars," but here they are in a race to be Broadway ready with a dance called a "four legged animal with two beating hearts."

"Nothing applies from what we know," says Chmerkovskiy, sweat seeping through his tank top. "It's like trying to be a great poet but in a different language. It's very hard."

The pair star in a revival of Luis Bravo's "Forever Tango," which traces the dance's birth on the streets of 19th-century Buenos Aires to its more modern manifestations. They will take over for Galoto and Horvath when the touring show opens at the Walter Kerr Theatre on Sunday.

Adding to the spiciness is that Smirnoff and Chmerkovskiy are former lovers, having been engaged for nine months in 2009. But both insist they've dealt with their personal issues and have moved on, although they use a more colloquial term than "personal issues."

In person, they are comfortable and playful, teasing each other, natural in their touch and easy to laugh. After a photographer takes their picture, Smirnoff playfully pleads: "Can you make sure I look good in all the pictures? It doesn't matter what he looks like."

When they dance, there is something effortless about their movement. The slender, beautiful Ukrainian-born Smirnoff seems to melt inside the torso of the hunky, muscular Chmerkovskiy, also born in the Ukraine. They think their intimate past can actually aid the tango, which should be sexy if done right.

"I think it helps. With every dance, you go to your experience, to your emotion, whatever you can relate to. I think with Maks, we both can go to a place where -" Smirnoff says.

"No one's been before," Chmerkovskiy interjects with a laugh.

"Exactly. We had our ups and we had the lowest of the lows and we can take that into the dance and make it than much better," his partner finishes.

"Aside from what transpired, I do have respect for her as a dancer. We went to a bad spot at one point or another but it's been documented: I've never lost respect," he adds. "I've always been looking forward to one day get this out of the way."

Unlike the American ballroom tango with its big, showy, dramatized staccato movements that include a rose in the teeth, the Argentinian version is often improvised and much more seductive. Learning the salsa or waltz is a walk in the park by comparison.

"It can be fun. It can be sad. It can be dramatic. It can be entertaining. It can be anything you want it to be, based on the music and choreography," says Smirnoff. "So I think it's one of the hardest dances."

They're learning from tango pros in Galoto and Horvath, though their English is not as strong as their leg work. Lessons have become more about two pros wordlessly showing another set of pros how to express themselves.

"Time has to pass for you to get it. There's no way around it. For us, we have to let go of structures and counts and steps and all that and just try to understand their language and start speaking it," Chmerkovskiy says.

He laughs that he and Smirnoff have danced the tango plenty of times on "Dancing With the Stars" - she went all the way and won the mirrorball trophy with J. R. Martinez in Season 13 - but now they're really learning it.

"We've spent the last eight years pretty much on the show finding a way to dumb down - no disrespect, that's the only way to do the show - what we do and package it in a very clear way. There's no way to package this. We have done Argentine tango on the show, which goes to show what kind of tangos we did versus what the real one is," he says.

Both are Broadway veterans, having co-starred in "Burn the Floor" in 2009. But this time they seem to be more fearful of the challenge and more apprehensive about getting the approval of their teachers.

"It's important for us to know that we gave 100 percent. And to know that we're able to deliver. Not just for 'Forever Tango' and Broadway but for these guys who've spent days with us trying to get us to the level that we need to be."

"Exactly," says Chmerkovskiy, gesturing to his tango tutors. "This is what I said to both of them: "'Look, I just don't want to be a bad tango dancer.'"

"Is there hope for us?" Chmerkovskiy asks his teachers.

"Yes. Of course," Galoto answers sweetly. "There is always hope."