Abstract: This article reports a case of a 48-year-old male patient whose initial presentation was cardiaopulmonary arrest. Despite undergoing a comprehensive series of examinations, including electrocardiography, chest and cranial computed tomography (CT), emergency coronary angiography, aortic CT perfusion imaging, bedside echocardiography, Holter monitoring, and whole-exome genetic sequencing, the etiology of the cardiac arrest remained unclear. The diagnosis of concealed hypertrophic obstructive cardiomyopathy (HOCM) was ultimately established based on cardiac magnetic resonance imaging (CMR) and stress echocardiography, following the systematic exclusion of coronary artery disease, hypertension, and Fabry disease. This case highlights that concealed HOCM in young and middle-aged adults can present as cardiaopulmonary arrest. For cases with echocardiography showing only mild hypertrophy and no resting left ventricular outflow tract obstruction making them prone to misdiagnosis, further evaluation with CMR and stress echocardiography is warranted to establish a definitive diagnosis after ruling out common causes of cardiaopulmonary arrest.