Abstract Funding Acknowledgements Type of funding sources: None. Background Considering that myocarditis is implicated in 5-15% of all exercise related sudden cardiac deaths in athletes, following a novel viral pandemic, the identification and risk-stratification of affected athletes remains an important priority. Given its widespread availability, the inclusion of a 12-lead electrocardiogram (ECG) is common to all consensus-based protocols from North America and Europe. However, a single cross-sectional ECG is problematic because several physiological repolarisation changes are also common manifestations in individuals with myopericarditis. Purpose The aim of our study was to report on the prevalence and diagnostic significance of de-novo ECG patterns following COVID-19 infection in a well-defined cohort of elite soccer players in the English, Dutch and Brazilian leagues. Methods In this multicentre observational study, between March 2020–May 2022, we evaluated consecutive athletes with COVID-19 infection. ECGs were reported in accordance with the International recommendations for ECG interpretation in athletes. The following patterns were also considered abnormal if they were not detected on the pre-COVID-19 infection ECG: PR-segment depression, new J-point and ST segment elevation, low QRS voltages, QRS fragmentation, new ST-segment depression, new T-wave inversion, biphasic T-waves and a reduction in the T-wave amplitude by 50% or T-wave flattening. Athletes exhibiting de-novo ECG changes underwent cardiovascular magnetic resonance (CMR) scans. One club mandated CMR scans for all players (n=30) following COVID-19 infection, despite the absence of cardiac symptoms or de-novo ECG changes. Results 511 soccer players (median age 21-years, IQR:18-26-years) were included, of which 88% were male and 58% white. 17 (3%) athletes demonstrated de-novo ECG changes, which included, a reduction in T-wave amplitude in the inferior and lateral leads (n=5), inferior leads (n=4) and lateral leads (n=4); inferior T-wave inversion (n=7), and ST-segment depression (n=2). 15 (88%) athletes with de-novo ECG changes revealed CMR evidence of inflammatory cardiac sequalae. All athletes who underwent a mandatory CMR irrespective of illness severity or ECG findings, had normal findings. Athletes revealing de-novo ECG changes, had a higher prevalence of cardiac symptoms (71% v 12%; p<0.0001) and longer median symptom duration (5-days, IQR:3-10) compared with athletes without de-novo ECG changes (2-days, IQR:1-3; p<0.001). Among athletes without cardiac symptoms, the additional yield of de-novo ECG changes to detect cardiac inflammation was 17%. Conclusions 3% of athletes demonstrated de-novo ECG changes post COVID-19 infection, of which 88% were diagnosed with inflammatory cardiac sequalae. Most affected athletes exhibited cardiac symptoms; however de-novo ECG changes contributed to a diagnosis of cardiac inflammation in 17% of athletes without cardiac symptoms.