Joshua Hughes of Ashburn, plays with his daughter, Jaclyn, Hughes, who was born with a heart defect. (Marvin Joseph/THE WASHINGTON POST)

hours after their son Tristan was born, Stephanie and Scott Wright were looking for a priest.

“We just thought, ‘He was born with half a heart — it’s over. It’s done,’ ” Scott Wright said.

But congenital heart disease, almost always a death sentence just a few decades ago, now has a 98 percent survival rate, said Gerard Martin, a pediatric cardiologist at Children’s National Medical Center. On Saturday, he was surrounded by Tristan, other children and their families at a party hosted by the hospital at the National Zoo.

Part reunion, part support group, part inspiration, part carnival, “it’s just a chance to celebrate life,” Martin said.

Lisa Gandy, who works at the hospital, saw Tristan and wrapped him in a big hug. “You’re getting so big!” she said.

Ximena Lugo, adjusts the cap on her daughter, Nicolle, right, who was born with a heart defect. Nicolle's twin sister, Sophia, does not have a heart defect. (Marvin Joseph/THE WASHINGTON POST)

Tristan, 5, with a fuzz of blond hair and lips turned bright blue from a slushie, pulled up his “U.S.A. All The Way!” T-shirt to show the thick scars from three surgeries, typically done early in life to treat hypoplastic left heart syndrome. They stretched from his collar bone halfway to his belly button.

“There’s your heart zipper!” said Joshua Hughes of Ashburn, whose daughter Jaclyn has a similar condition.

Starting kindergarten

Tristan started kindergarten in Dale City last week, with his mom making sure all the teachers knew about his heart condition and assuring them that she could be at the school in moments.

“It's in the back of your head all the time,” she said, but he’s a regular little boy who plays T-ball, goes to swim lessons and plays with friends. “He gets tired faster than the average 5-year-old,” she said.

Tristan held up a big stuffed dog the hospital gave him. He had already named it Lighty-up Doggie. “His back lights up,” he explained. At the zoo, he watched the prairie dogs popping in and out of holes, and the lions stalking through the grass.

At the center of the zoo, under a big tent, he sat with Jaclyn, eating her potato chips. The families met when he was having his second surgery and she was having her first. They have been friends ever since.

“She was just in the hospital, and he had to go see her,” Stephanie Wright said.

“She was asking for him,” Scott Wright added, cutting up pieces of hot dog for Tristan and his little brother, Drayk. “It’s nice to be here,” he said, looking around at kids coloring and plastering themselves with stickers. “It gives you a sense of hope, I guess. Lets you know you’re not alone.”

Stephanie Wright pointed across the crowd. “Look, Tristan! There’s Dr. Frank!”

Lowell Frank was a cardiology fellow when Tristan was in the hospital. Tristan liked the red Chuck Taylor sneakers that Frank wore under his scrubs, and Frank spent a lot of time with him. Tristan ran across the grass and tugged at Frank’s shorts. Frank’s face lit up, and he crouched down to talk with Tristan, teasing him about his black skateboarding sneakers.

Is that your doctor? someone asked when Tristan went back to his lunch.

“No,” he said. “He’s one of my friends!”

Stephanie Wright was talking with Sandra Hughes. Joshua Hughes helped Tristan build a balsa-wood plane, and Tristan held it aloft, running circles around the picnic table.

‘A happy kid’

“He is such a happy kid,” Scott Wright said, a boy who loves the pool, loves slides, loves playing “fetch,” with his dad chasing balls he throws. He followed Tristan and the Hugheses onto the grass to play with a bright green beach ball. “You live in the moment,” he said. “Today is great. Today is good. I’m blessed. I try not to think about the future.

“At some point, he will need something else. He’ll enter heart failure.”

At that point, the Wrights hope, there will be some medicine, a transplant, or something else that will keep Tristan going.

“They say you only get so many heart beats, so make every one count,” Scott Wright said. “Well, he has half as many.”

Tristan kicked the ball, laughing as he watched it soar up toward the orangutans, and his father went chasing after it.