The cause of Knox MacEwen’s tragic death was later determined to be hypertrophic cardiomyopathy, a condition characterized by the thickening of the heart muscle. This condition can sometimes go undetected and can lead to sudden cardiac arrest, especially during physical exertion like running a 5K race. It’s a heartbreaking reminder of the importance of regular medical check-ups and screenings, especially for young athletes, to ensure their heart health and safety during strenuous activities.