Aneurysm of the membranous interventricular septum

CASE SUMMARY The patient is a 19-year-old male with a past medical history of a repaired ventricular septal defect (VSD) and cardiac arrhythmia who presents with shortness of breath. Membranous interventricular septal aneurysms have been associated with ventricular septal defects and outflow abnormalities, such as transposition of the great vessels.3,4 Even though these patients are often asymptomatic, they can be a source of arrhythmias or thrombus formation.5 The aneurysms can also protrude into the outflow tract of the right ventricle, resulting in obstruction.1 Transthoracic echocardiogram as a method of diagnosis is limited.