Cardiac arrest occurs in 4 to 14 per 100 000 apparently healthy young adults aged 18 to 40 years worldwide each year. Cardiac arrest in apparently healthy adults younger than 40 years may be caused by cardiac disease or noncardiac causes. Based on autopsy studies, 55% to 69% of young adults who die after a cardiac arrest have a heart rhythm disorder or structural heart disease such as coronary artery disease or hypertrophic cardiomyopathy. ➡️ Learn more about the causes, risk factors, evaluation and treatment, and bystander instructions for cardiac arrest in apparently healthy young adults in this JAMA Patient Page: ja.ma/43lDjx2