At the present time there are no devices available to measure recirculation, oxygenator blood volume and cardiac output in patients on extracorporeal membrane oxygenation. The study uses an external monitor, laptop computer, clamp on flowsensors and ultrasound dilution technology to measure blood flow. Measurements are made by injecting 0.5 - 1 ml/kg of sterile isotonic saline into the patient's extracorporeal circuit. The subject will be monitored throughout the measurements. The measurements will be coordinated with the regular care of the extracorporeal circuit.