Extracorporeal membrane oxygenation (ECMO) is a salvage therapy in acute cardiac failure and/or severe respiratory failure. In this case report the importance of cannula positioning during veno-venous ECMO is exemplified. The use of echocardiography and its advantages compared to plain chest radiograph will be shown. This case reflects a 5-month-old boy who acquired a severe viral pneumonia leading to respiratory failure and ECMO treatment. Extracorporeal membrane oxygenation was performed via a dual lumen cannula correctly placed in the right atria according to a chest radiograph. During the first day of treatment the patient's arterial saturation was not satisfying. Assessment revealed that a part of the ECMO flow was recirculating. Echocardiography was used to optimize the cannula position, and thus, rapidly improving the patient's oxygenation. A persistent left superior vena cava and its effect on the central hemodynamics were also objectified. This case illustrates important considerations in daily ECMO treatment: the benefit of direct echocardiographic competence at all times during the day, the importance of understanding central blood flow dynamics, to adjust the cannula-position accordingly, and to address situations outside the ordinary with a physiologic approach.