Jenny Simpson, the 39-year-old American Olympic medallist and former 1500m world champion, has announced she will not return to running after being diagnosed with a rare inherited heart condition. In June, Simpson collapsed while pacing a mile group at a pop-up event in North Carolina, suffering a cardiac arrest that required CPR and an automated external defibrillator. She was transported to UNC Rex Hospital in Raleigh, where she went into cardiac arrest again.

Doctors diagnosed Simpson with ARVC (arrhythmogenic right ventricular cardiomyopathy), a genetic condition where proteins that hold heart muscle cells together malfunction, causing muscle cells to die and be replaced by fatty and scar tissue. This thins and stretches heart chamber walls, impairing the heart's ability to pump blood. Simpson stated that returning to running would be dangerous, declaring "that chapter has ended."

Simpson won gold at the 2011 World Championships and bronze at the 2016 Olympic Games in Rio, adding silver medals at the 2013 and 2017 World Championships. She retired from competitive racing at the end of the 2024 season, expressing gratitude for her career: "I experienced everything - from the trenches of training to standing on the top of the podium while our national anthem filled the stadium."