A 6-year-old Georgia boy collapsed on a baseball field and later died from a heart defect he had since birth, his mother and his coach said Monday.

Brantley Chandler, a first-grader from Rock Springs in far northwest Georgia, was lining up for a picture with teammates when he suddenly fell and struggled to breathe Thursday night.

An ambulance rushed him to a children's hospital in nearby Chattanooga, Tennessee, where he could not be revived.

Brantley Chandler, who died of a heart attack during team photos. Courtesy Chandler Family

Brantley was born with a rare congenital heart defect — hypoplastic left heart syndrome — and had three open-heart surgeries by the time he was 2, according to his mother, Megan Bryson.

In such cases, the first surgery occurs shortly after birth, the second one at about 4 to 6 months of age, and the final at about 2 to 4 years of age, said Dr. Achiau Ludomirsky, pediatric cardiologist at Hassenfeld Children’s Hospital at NYU Langone.

“The goal of the three surgeries is to convert the right ventricle into the systemic ventricle of the body,” Ludomirsky added.

HLHS is a severe defect in which the left side of the heart is underdeveloped. The left side of the heart pumps oxygenated blood to the body — but when it's underdeveloped, that doesn't occur and a baby's organs don't get the oxygen they need to function properly.

The condition is found in four to 16 of every 10,000 live births in America, according to Cleveland Clinic data.

“There was no sign or symptom, which I was told was a major possibility — that it could be an instant heart attack,” Bryson told NBC News on Monday. “I never told him or explained it to him,” she said of the heart defect. “So, he never thought he was any different from the rest of the kids.”

“He was just a normal kid, running around town, running around the house,” Bryson, who is a licensed practical nurse, said.

On the baseball field, the youngster was obsessed with being the fastest player on the team, his coach, Jamie Chapman, said. His favorite drill was to get timed as he circled 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,” Chapman said.

Brantley was with his fellow players, who were all 7 and 8 — about one year older than him — for the Mustangs team pictures Thursday night. They had snapped all the individual pictures when Chapman tried to round up all 12 players for the team shot.

“So I'm counting them out, and I said, `Man, we only have 11. Who am I missing? Where's B (Brantley)?' I look up and there he was, just running the bases,” Chapman recalled. “That was one of my last memories of him.”

As the photographer was lining up the players for the team picture, Brantley grabbed his back and fell forward, according to Chapman. The coach and the child's grandfather called 911.

The Mustangs didn't get to take their team picture until Saturday, when Brantley's teammates attended his viewing.

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

Brantley is survived by three younger half-siblings — two sisters and a brother.

Doctors do not believe that playing baseball played a role in the heart attack.

“Competitive sports are not recommended, but baseball at 5 or 6 years old wouldn't qualify as an overly vigorous sport that Brantley shouldn't have been allowed to play,” Ludomirsky said.

“I’m sure he got very good, great care and we have to think about a child’s quality of life.”

Even though Brantley's family was well aware of his heart condition, he seemed to barely notice the surgical scars on his chest and lived like any other youngster in northwest Georgia, according to his mother.

“I did think about it every so often because of what the future held. I never made him live in a bubble; he was outdoors as much as possible, playing baseball and, anything he wanted to do, he was doing it,” Bryson said. “He had a very good, nearly 7 years of quality life.”

Ludomirsky agrees but also credits modern medicine for extending Brantley's life.

“He got three surgeries with great results. He was alive until 6 years old,” he said.

“It's really unfortunate and there’s no way to console the parents. Prior to these new surgeries, that might not have been possible.”