TUSTIN -- There's something different about Chance Mitchell.

At 6, he's an architecture buff who keeps a scale model of the Eiffel Tower at his Temecula home. He uses his Lego blocks and cardboard to construct his own super-structures. He also has to wear a pacemaker for the rest of his life.

And there's just one building model he's got to have: Saudi Arabia's Burj Dubai Tower, the 160-story mega-skyscraper that will be the world's tallest building when it's completed at the end of this year.

On Friday, Chance got his wish and more.

He was the latest recipient of the Make-A-Wish Foundation of Orange County and the Inland Empire. At the organization's Wish House in Tustin, he accepted a 4-foot scale model of the Dubai Tower built especially for him by Minnesota-based Red Eye ARC, as well as autographed original drawings of the structure and a full-color photo book by architect Adrian Smith. But the day's highest point was the half-hour video Web chat with Smith himself.

"What a blessing," said Chance's mother, Melissa Mitchell. "What a blessing. To share his life with us, this is amazing. I mean, this is a world-renowned architect taking time out of his life for a 6-year-old."

Chance has atrial septal defect, a condition in which the septum -- the wall separating the heart's left and right chambers -- has a hole. That causes the oxygen-rich blood from the left side to flow into the right, mixing with the oxygen-poor blood and returning to the lungs with it. That decreases the heart's efficiency, because a mix of oxygen-rich and -poor blood is being returned to the lungs, instead of all oxygen-poor blood.

Congenital cardiovascular defects such as ASD occur in about 1 percent of births, according to the American Heart Association.

Chance's condition hasn't cut his tall ambitions to become an architect. Melissa Mitchell said Chance became interested in the Dubai Tower about a year ago, during an Internet search for the world's tallest building.

During their chat, Smith fielded a range of questions from Chance, from the number of residents the building can hold (up to 10,000), to whether the project will meet its projected September 2009 deadline.

Dubai Tower will be completed by December, Smith said.

A second screen next to Smith featured a series of rotating images that showed the Dubai Tower during its various stages of progress.

"I learned a lot," Chance said after the chat.

His mom says he's always wanted to be a builder. "He's just an amazing, sensitive kid. He's very bright, and he's overcome a lot," she said.

Friday's events were also a welcome reprieve from the medical, financial and emotional turbulence in the family has endured, Melissa Mitchell said.

Chance, his mother and his 4-year-old sister Cadence all have congenital heart conditions. Collectively, they've undergone five open-heart surgeries and 10 cardiac catheter surgeries, and spent a combined 500 nights at the hospital.

Cadence's condition is the direst of the trio. Born with hypoplastic left heart syndrome, her heart's inability to fully develop its left side means she will need a heart transplant to survive.

The family's medical expenses have also pushed them to the brink of losing their home. And just last month, Melissa Mitchell was laid off. Friday and last week, when Cadence's wish to meet the Little Mermaid in Disneyland was granted by Make-A-Wish, were treasured moments of normalcy, she said.

In the minutes leading up to his Web chat with Smith, Chance raced around the Make-A-Wish Wish House, briefly pausing to share his feelings about architecture.

"I just like tall buildings," he said. "They're so cool."

Smith later praised Chance: "I'm really impressed with your interest at such an early age. It's a fun profession, it's a wonderful profession. Keep it up!"

"Thank you!" Chance said, beaming from his mother's lap as his father, Jonathan Mitchell, recorded the chat on his video camera.

The Foundation's original plan was to obtain the tower model for Chance. But Smith became interested in doing more than providing the tower blueprints to Red Eye ARC model builder Ryan Sybrant after hearing Chance's story, said Wish Coordinator Desiree Au.