The heart of rock 'n' roll is alive and drives a FedEx truck around Columbia Heights by day.

By night, onetime Mercury Records artist and former next-great-thing Mary Cutrufello still plays gigs -- not four or five per week, like when E Street Band member Danny Federici was her keyboardist and they did "The Tonight Show" together. Nowadays, Cutrufello plays just enough to keep her passion alive.

The Yale-educated rocker and country picker, 42, has always been a zealot on stage. She might even be more of one now, after being sidelined by vocal-cord damage in the mid-2000s.

Mercury was the big time. Unfortunately, her lone recording for the company, 1998's "When the Night Is Through," arrived right before Mercury was folded into the Universal Music Group. Cutrufello's big record deal ended just as it began.

"The only thing I could regret is that we all didn't get to become big rock stars," she said. "That's a pretty sorry regret."

She landed here in the fall in 2001, not long after wrapping a tour opening for the Allman Brothers. Little did she know that she would come here to lead the blue-collar lifestyle she had been singing about all those prior years.

Cutrufello started working the graveyard shift at the FedEx terminal in Mahtomedi shortly after her relocation, a packing job she intended as "a buffer" to make up for her lessening music income. But then, as she puts it, "One day I tried to sing, and nothing came out."

Her famously husky, powerful voice vanished in 2004 as the result of a polyp, a growth that prevented her throat from closing properly. Her two options were: "Get it surgically removed, or be quiet for a while."

Cutrufello chose the latter, halting her singing career and doing as little talking as possible for eight months. That's when she wound up with her own delivery truck at FedEx, a job in which she now takes great pride.

After undergoing voice therapy, she said her voice eventually came back 100 percent. However, she has obvious qualms about shredding her throat all night like she used to do. So she issued an acoustic EP and took to playing mellower gigs.

Enter "Fireflies Till They're Gone," the new EP that Cutrufello will promote with a release party Friday at the 331 Club. The six-song, all-twang collection features one tune apiece from Waylon Jennings and Willie Nelson, plus four originals.

"When my voice came back, I was singing with whole other level of nuance that really suited singing these kind of country songs," Cutrufello said. "Honestly, I wish I had this voice back when I was playing 200-plus shows a year."

Asked if she would like to give up her FedEx job and go back to playing music full time, she said, "I don't know. That might take away from the fun I'm having now."