Cardiac catheterization and percutaneous transvenous mitral commissurotomy using the Inoue technique were attempted in a 44-year-old woman with mitral stenosis. The pulmonary arterial wedge pressure was 25 mmHg, mean transmitral diastolic pressure gradient 20.3 mmHg, cardiac index 1.80 L/min/m2, and mitral valve area 0.70 cm2. After the diagnostic catheterization, the guide wire for the transseptal procedure was checked in the middle of the inferior vena cava (IVC). A 7-French end-holed Bermann catheter was then used to detect the course of the IVC. It was found that the IVC coursed along the left border of the 4th and 5th lumbar vertebrae, to the left of the abdominal aorta. At the upper border of the third lumbar vertebra, the IVC returned to the right side of the vertebra. In consideration of the inability to pass the Brockenbrough needle through the detoured infrarenal IVC and the risk of rupturing the vessel, the transseptal procedure and attempted percutaneous transvenous mitral commissurotomy were aborted. Therefore, the patient underwent open mitral commissurotomy instead.