Abstract: Catastrophic antiphospholipid syndrome (CAPS) represents the most severe clinical manifestation of antiphospholipid syndrome (APS), characterized by rapid onset of extensive thrombosis resulting in multi-organ failure and a markedly high mortality rate. The clinical presentations of CAPS exhibit considerable heterogeneity, often mimicking acute and severe conditions such as sepsis, thrombotic microangiopathy, or fulminant myocarditis (FM), which can lead to misdiagnosis. Notably, CAPS that presents with acute heart failure or myocarditis as its primary symptom is particularly uncommon, making early identification exceedingly challenging. This article examines a case of adolescent CAPS that was misdiagnosed as FM, systematically analyzing its clinical features, diagnostic considerations, and management strategies. The objective is to enhance clinicians' awareness of cardiac involvement in CAPS and to underscore the necessity of early antiphospholipid antibody screening and multidisciplinary collaborative treatment.