The Health Protection Branch of Health Canada and The Food and Drug Administration of the United States both recognize the need for controlled clinical trials in pediatric patients. To our knowledge, neither digoxin nor propranolol has been evaluated for pediatric use in a controlled trial in the context of SVT, yet both medications are used frequently. Therefore, this study is needed because digoxin and propranolol continue to be used as the most common therapy for prevention of recurrent SVT. There is a significant debate about their effectiveness, with a division between experts in the field and general cardiologists. There may be a large impact on patients if one medication is better than the other or has more adverse outcomes (e.g. hospital admissions). The results of this trial have significant potential for direct impact on infant health and provision of care in Canada and globally. This is evidenced by the large number of electrophysiologists endorsing the trial.