The Berlin Marathon last month was her fifth, but first since badly breaking her ankle the previous year. But she was moving along well with the crowd of some 54,000 other runners.
She was a few miles from the finish, just before mile 22, when she encountered a runner on the ground on his side. She immediately switched into professional mode and checked his pulse.
"All the sudden, he turned blue and stopped breathing. I lost the pulse on his neck," Pierko said.
She determined he had gone into cardiac arrest, so she immediately began chest compressions, as she demonstrated on this pillow, with 100-120 compressions a minute in the middle of the chest.
"Every minute counts. If there's a delay, the chances of survival go down 7-10% every minute," Pierko said.
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While she continued chest compressions, she got someone in the crowd to give mouth to mouth. Another called for paramedics. And within minutes, the runner's pulse and regular heartbeat returned.
So, with her work apparently done, Pierko realized she had a race to finish. She did finish, and despite stopping for nearly five minutes, she still ran her fastest marathon.
"It was very important race for me on so many levels, it turns out," Pierko said.
Patient privacy laws keep the name of the patient Pierko worked on anonymous. Nevertheless, she can say he is in his late 60s, and thanks to her help, he survived.