The use of extracorporeal membrane oxygenation (ECMO) for short-term mechanical circulatory support in patients with systemic circulatory collapse has increased.¹ Venoarterial (VA) ECMO is the most common application, and pulmonary edema is one of the complications that can occur due to a failing heart. This makes weaning or bridging a durable left ventricular (LV) assist device or heart transplantation difficult. Pneumonia following pulmonary edema is associated with a high mortality rate,² and in this situation, transseptal left atrial (LA) decompression is often applied. In general, since the catheter for transseptal LA decompression is directly connected to the venous drainage limb of the ECMO circuit, it is often difficult to effectively control blood flow; therefore, there may not be sufficient LA decompression. Herein, we report a case in which pulmonary edema was improved by controlling the blood flow rate of the transseptal LA catheter using an additional ECMO pump without an oxygenator for effective LA decompression.