The mother of a 6-year-old boy who collapsed and died of an apparent heart attack during his team’s baseball pictures last week, said he was born with a rare congenital heart defect. Brantley Chandler, who is being remembered for his love of baseball and his dog, “Boss,” was born with Hypoplastic Left Heart Syndrome, which affects normal blood flow through the heart.

The condition, which according to the Centers for Disease Control and Prevention (CDC), requires surgery soon after birth and affects a number of heart structures, including the left ventricle, mitral valves, the aortic valve and a part of the aorta. It may also cause an atrial septal defect, which opens a hole between the left and right upper chambers.

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The condition is estimated to affect 960 babies born in the U.S. each year, with no known risk factors or causes. Infants who undergo corrective surgery for the condition are not considered cured and may have lifelong complications. Patients may even need a heart transplant if complications arise after surgery.

The first-grader’s obituary said he “loved playing baseball and was the catcher for the Rock Spring Mustangs. When not playing baseball, Brantley could be found enjoying what the outdoors had to offer.”

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Megan Chandler, who posted a heartbreaking tribute to her son on Facebook after his March 28 death, told News Channel 9 that there is no way she could’ve prepared for her son’s sudden passing.

“I seriously don’t know what to do or how to live,” she posted, in part.