Emma Aronson, a 17-year-old star athlete from Missouri, had a heart attack and died while playfully racing against friends in a neighborhood pool Friday night.

"She was racing in the pool against the boys and, of course, she wanted to beat them—and most of the time she did," said her devastated mother, Laura. "She got to the edge and said, in a very small voice, 'I'm so tired,' and then that was it."

Aronson's friends tried to give her first aid, but she was unconscious and died.

The teen was a competitive and talented varsity basketball player. Her sudden death was a shock for both her family and friends, according to KCTV 5 News.

The family said that Aronson had a heart condition and underwent surgery when she was four, reported KMBC News.

"Emma, I know your [sic] up in heaven and I pray you don't see my pain because I know it would hurt you," wrote her mother in a moving Facebook message. "My heart hurts so much and I just wish I could kiss your beautiful face one more time. If you saved even one life I know you'd do it again. I know it's not forever and we will be together again, but for now the tears will flow and the sadness will remain. My life will never be the same."

Her mother revealed that her daughter wanted to save lives—and she was able to do that by donating her organs to at least 50 people, reported Fox 4 Kansas City.

The family is still waiting for an autopsy report from the Jackson County Medical Examiner's Office. Police investigating her death are speculating either drowning or cardiac arrest.

A GoFundMe page was set up to help Aronson's family with medical and funeral expenses.