Mesalamine-containing products are considered first-line treatment for inflammatory bowel disease. Myocarditis is recognised as a very rare possible side effect of these medications, but has not often been described in the paediatric population. We present a case of an adolescent with Crohn’s disease who presented with myopericarditis after recent initiation of Pentasa. Once identified as the causative agent, the drug was discontinued, with subsequent normalisation of troponin and improvement of function. This case identifies the importance of prompt evaluation, diagnosis, and treatment of paediatric patients receiving mesalamine-containing medications that present with significant cardiovascular symptoms.