Aims: This thesis investigates the performance of the ECG in identifying young individuals at risk of sudden cardiac death and address the current gaps in our knowledge of the ECG as a screening tool. In particular, this thesis focusses on: 1) Performance of the contemporary ECG interpretation criteria in young competitive athletes, with particular emphasis on the workload and cost of additional investigations required following screening. 2) The reliability of ECG interpretation in athletes amongst cardiologists 3) The prevalence of cardiac conditions, outcomes and financial implications of a nationwide ECG screening programme in young, predominantly non-athletic individuals. Methods: All participants were recruited through the Cardiac Risk in the Young screening program in the United Kingdom. Almost 32,000 young individuals (including nearly 5,000 competitive athletes) underwent ECG screening to identify cardiovascular disease associated with sudden cardiac death. Main Results: 1. The most recent ECG interpretation criteria in athletes, the ‘international recommendations’, are valid in young competitive athletes and are associated with an 86% relative reduction in the number of abnormal ECGs and a 22% relative reduction in the cost of screening compared.to the 2010 ESC recommendations. 2 inter-observer reliability for ECG interpretation among sports cardiologists is moderate but is higher compared with non-sports cardiologists. 3. Non-sports cardiologists are 5-12 times more likely to request additional investigations following screening compared to sports cardiologists. 4. The prevalence of cardiovascular disease associated with young sudden cardiac is 0.3%. 5. Inclusion of the ECG to a health questionnaire improves the diagnostic yield for disease detection in young individuals by 5-fold, and is associated with a 37 % cost saving to identify these diseases. Conclusions: This thesis highlights pertinent financial issues in relation to preventing young sudden cardiac death through ECG screening, and provides useful information relating to best practice to better inform healthcare policy.