Biting her lip and choking back tears as they played The Star-Spangled Banner, she looked in a state of shock after she had beaten former world record holder Leisel Jones of Australia into second.
"It's been a long road to get here. I cannot believe what has just happened. I've won a gold medal," said the fresh-faced 21-year-old. "I was a little bit in shock.
"I was shaking a little bit up there. But it is great to be there to hear the national anthem."
The softly-spoken swimmer, who captured the silver in the 100 breaststroke after being a late replacement for Jessica Hardy, who had failed a doping test, made light of her astonishing progress since the surgery.
"It was a small heart procedure to take care of things and get back in training.
"I definitely think I exceeded my expectations. I already have two medals and I came here for one event. Things are going great," Soni said.
The University of Southern California communications student said she had been confident she would be able to win a medal after finishing behind Jones in the 100.
"As I get through the meet, it starts to flow better and everything goes faster," she said.
"I have only raced her three or four times in the past. Each time I remember how she went out faster and it kinda got into my head."
Soni certainly was living the classic American dream.
Her parents, who are from Hungary and Romania, came to the United States before she was born to build a new life.
"I guess this is what it is all about. I wish they could be here. They are back home in Arizona watching."