Study objective: To validate a non-invasive cardiac output monitor in pediatric cardiac surgery patients. Design: Prospective trial. Setting: Operating room. Patients: 20 pediatric cardiac surgery patients ASA physical status 3 and 4. Interventions: Aesculon noninvasive cardiac output monitor was used and compared to the cardiac output derived from the Fick equation. Oxygen consumption was measured and blood samples were taken from the arterial line and from the superior and inferior vena cava. Measurements: Noninvasive cardiac output and cardiac index and Fick cardiac output and cardiac index. Oxygen consumption was measured by the TreyMed metabolic monitor. Blood samples were simultaneously drawn from the arterial line and from the superior and inferior vena cava purse string sites by the surgeon, prior to commencing cardiopulmonary bypass. Another data set was obtained right after termination of cardiopulmonary bypass. Results: There was a direct, significant relationship between Fick CO/CI and NICOM CO/CI measurements. More dispersion is detected when the magnitude of the measure increases, i.e., for older and larger patients. Conclusions: There is a strong correlation between the cardiac output values derived from the Fick equation and the Aesculon non-invasive cardiac output monitor. (C) 2017 Elsevier Inc. All rights reserved.