Unexpected twist: large marginal branch occlusion of the left circumflex artery unveiled by immediate and pivotal cardiac magnetic resonance imaging in a 19-year-old with suspected myocarditis-a case report.

Background: Myocarditis and myocardial infarction in young patients can present with overlapping symptoms, posing a diagnostic challenge. Advanced cardiac imaging, particularly cardiac magnetic resonance imaging (MRI), plays a pivotal role in distinguishing between these entities. Case summary: A 19-year-old male presented with a 5-week history of fever, general weakness, and new atypical chest pain, raising the suspicion of myocarditis. Immediate cardiac MRI revealed signs of lateral wall ischaemia. Coronary angiography confirmed an occlusion of a large marginal branch of the left circumflex artery. Pathological analysis of the retrieved thrombus indicated a septic embolism, and further investigations confirmed endocarditis due to Discussion: This case highlights the essential role of early cardiac MRI in guiding clinical decision-making, particularly in young patients with non-specific symptoms. Although rare, endocarditis-related septic embolism must be considered in the differential diagnosis of acute myocardial infarction in this population.