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BACKGROUND: Aneurysm of the muscular interventricular septum is a rare entity as compared to the membranous part. Only a few cases of dissecting septal aneurysm have been reported in literature. Two-dimensional echocardiography is the initial diagnostic modality with ECG-gated CT and MRI being non-invasive imaging modalities for comprehensive evaluation. The complications can arise from chronic pressure erosion of the intervening septal myocardium, leading to left-to-right shunting in the form of ventricular septal defect and paradoxical thromboembolism. Radiologists should be aware of imaging findings of interventricular septal aneurysm, because of its rarity of occurrence and complications. CASE REPORT: A 48-year-old male patient presented to a cardiology department with complaints of intermittent chest pain, palpitations and exertional dyspnoea. CT angiography revealed a wide-mouth large aneurysm arising from the mid and apical portion of the interventricular septum dissecting into the basal part. There was associated significant bowing (>15 mm) of the septum and mild obliteration of the right ventricular cavity. Myocardium surrounding the aneurysm was identified with no associated ventricular septal defect (VSD). No evidence of intraventricular clot was found. Catheter angiography confirmed the CT angiographic findings. CONCLUSIONS: Radiologists should be aware of imaging findings of interventricular septal aneurysm, because of its rarity of occurrence, complication in the form of thromboembolism, dissection and intracardiac shunting and mass effect over adjacent cardiovascular structures. Careful scrutiny is essential to avoid labelling of these cases as cardiac masses.