As doctors get increasingly creative about fixing children's heart problems, they are creating a whole new population: kids who grow up with heart problems.

That's opening up a whole new field to serve people like Kristina Diaz, of Lake Stevens. She's having a milestone birthday. She just turned 21.

But this isn't any ordinary 21st birthday beerfest, because it's extraordinary that Kristina is alive and well.

Few understand how uncommon it was for kids with congenital heart defects to live to adulthood. Kristina is one of the first.

"I definitely feel so grateful that I know, just 40 or 50 years ago, if I had had this problem, I probably wouldn't be here right now," she said.

Kristina was born with Tetralogy of Fallot, a condition where the heart has multiple problems, needing multiple surgeries. It made her different than other kids.

"It didn't really affect me much until I got to middle school age," she said. "I remember not being able to keep up with my friends, and wanting to do sports like volleyball and cheer, and I couldn't!"

"When I wore more low-cut things, they'd be like what happened?! I'd say oh yeah, I had heart surgery, and they're like, what?" she said.

Her open heart surgery scar became a badge of honor, as she grew older and wiser.

KING

Kristina just turned 21.

At 19, she stopped going to Children's Hospital.

"I just figured, I'm an adult. Every time I'd go to Children's Hospital - and I love Children's Hospital - but they'd be like, so where's Kristina?" she said. "I'd be like, I am Kristina, it's me!"

By going to the University of Washington Medical Center, Kristina is helping start a whole new field in cardiology. She's too old to keep going to a Children's Hospital, but not nearly as old as the typical heart disease patients seen at regular hospitals.

So the UW started a new program to help the growing number of Kristinas out there.

Karen Stout heads up the new transition team. Part of her challenge is balancing Kristina's care with her increasing independence.

She recently told Kristina not to move to South Carolina with her boyfriend. Not yet - she just had open heart surgery a few months ago, and needs watching.

But at 21, there's still much to celebrate.

"I just feel better, and I'm going to be able to go out and do … just experience life!" she said. "And I'm so excited to go do that. It's gonna be great!"