Mesalazine is a commonly used first-line therapy to treat acute mild to moderate ulcerative colitis (UC). Myocarditis is a rare complication of inflammatory bowel disease. This is a case report of a 19-year-old female with myocarditis induced after commencing mesalazine for UC. She was admitted with pleuritic-type chest pain associated with severe dyspnoea and was hemodynamically unstable during admission. She had elevated troponin and N-terminal pro-B-type natriuretic peptide. Transthoracic echocardiogram (TTE) results suggested there was evidence of myocarditis with reduced ejection fraction, which was later confirmed by cardiac magnetic resonance imaging. There was a rapid improvement of cardiac status after stopping mesalazine within two weeks.