OBJECTIVE To determine the accuracy of electrocardiogram (ECG) interpretation by pediatric emergency physicians through comparison with a pediatric cardiologist and to determine the intrarater and interrater reliability for pediatric emergency physicians and cardiologists. METHODS This was a prospective cohort study in which pediatric emergency physicians ordering an ECG completed a standardized questionnaire. The same emergency physician, a second emergency physician, and a pediatric cardiologist also completed the questionnaire for all ECGs at a later time. A randomly selected subset of ECGs was also interpreted by the same cardiologist and a second pediatric cardiologist. Major outcome variables were (1) whether the ECG was normal or abnormal, and if abnormal, (2) whether the abnormality represented a minor or major concern, and (3) whether the ECG warranted referral to a pediatric cardiologist. RESULTS For pediatric emergency physicians, the intrarater and interrater kappa values were 0.56 and 0.24 for the presence of an abnormality, 0.49 and 0.36 for level of concern, and 0.63 and 0.25 for need of cardiology follow-up. For pediatric cardiologists, the intrarater and interrater kappa values were 0.82 and 0.92 for the presence of an abnormality, 0.71 and 1.00 for level of concern, and 0.82 and 0.91 for need of cardiology follow-up. A comparison of the initial emergency physician and cardiologist interpretations yielded kappa values of 0.42 for the presence of an abnormality, 0.16 for level of concern, and 0.31 for need of cardiology follow-up. CONCLUSIONS When compared with interpretation by a pediatric cardiologist, ECG interpretation by pediatric emergency physicians was relatively inaccurate; intrarater and interrater agreement among emergency physicians was good and poor, respectively, and the intrarater and interrater agreement among pediatric cardiologists was excellent.