A young athlete collapses on the field; autopsy shows a massively thick septum. This is hypertrophic cardiomyopathy — genetic sarcomere mutation thickening the septum, obstructing outflow during exertion → fatal arrhythmia. It is the commonest cause of sudden cardiac death in young athletes — screening (family history, ECG, echo) before competitive sports saves lives; implantable defibrillators protect the diagnosed. The tragedy is preventable — the thickened heart announces itself on echo long before it kills.