A 45-year-old asymptomatic man diagnosed with asymmetric septal hypertrophic cardiomyopathy was referred for follow-up at the Instituto do Coração (InCor), São Paulo, SP, Brazil. The patient was using atenolol 100 mg/day and had no history of coronary artery disease. Physical examination findings were normal. Electrocardiography showed left ventricular overload and a first-degree atrioventricular block. Echocardiography confirmed hypertrophic cardiomyopathy with the left atrium measuring 52 mm (volume, 54 mL/m²), septum measuring 26 mm, posterior wall measuring 17 mm, left ventricle end diastolic diameter (LVDD) of 40 mm, and left ventricular ejection fraction of 65%. There were no signs of outflow obstruction. Mild mitral valve regurgitation and moderate diastolic dysfunction (E/e' ratio, 17) were noted. This test identified a protrusion in the basal segment of the inferolateral wall measuring 26 × 17 mm apparently containing all ventricular wall layers and presenting contraction, aspects compatible with a congenital diverticulum and differentiating it from a localized myocardial aneurysm.