Posing in his new uniform and smiling from ear to ear, young Brantley Chandler couldn’t have been more pumped to get his baseball season started.

“He loved playing…and was the catcher for the Rock Spring Mustangs,” his family says in his obituary.

Last week, while taking photos with his team in north Georgia, Brantley collapsed and died of a sudden heart attack. He was only 6-years-old.

“There was no sign or symptom, which I was told was a major possibility — that it could be an instant heart attack,” explained Brantley’s mother, Megan Bryson, in an interview with NBC News.

According to her, Brantley was born with a rare congenital heart defect known as hypolastic left heart syndrome, or HLHS.

“As the baby develops during pregnancy, the left side of the heart does not form correctly,” the CDC explains on its website, noting how HLHS “affects normal blood flow through the heart.”

“I never told him or explained it to him,” Bryson said of the birth defect. “So, he never thought he was any different from the rest of the kids.”

In his obituary, Brantley’s family described him as an “outgoing little boy” who was in the first grade at Chickamauga Elementary School in Chickamauga, Ga.

“When he was not playing baseball, Brantley could be found enjoying what the outdoors had to offer,” they said. “He loved Hunting, fishing, spending time with his hunting dog “Boss”, riding four wheelers, and playing in the mud getting his boots dirty!”

HLHS is reportedly found in four to 16 of every 10,000 live births, according to Cleveland Clinic data. But Brantley never let it slow him down.

“He was just a normal kid, running around town, running around the house,” his mother said, recalling how he also loved to run the bases. “If he didn’t like his time, he’d say, ‘Let me do it again,’ and he’d take off running the bases again.”

Brantley’s teammates wore their baseball uniforms to his funeral on Sunday, according to NBC.

“Some of the kids have not really experienced death before, so they don’t really know what’s going on,” explained coach Jamie Chapman. “Maybe it’s a good thing they don’t get it yet.”