A mock circulation system has been developed to approximate key anatomic features and simulate the pressures and flows of an infant. Pulsatile flow is generated by 10 cc pulsatile ventricles (Utah infant ventricular assist device). Systemic vasculature is mimicked through the use of 3/8” ID bypass tubing with two flexible reservoirs to provide compliance. Vascular resistance, including pulmonary, aortic, and major branches, is controlled via a series of variable pinch clamps. The coronary branch has a dynamic resistor so that the majority of flow occurs during diastole. The system is instrumented to measure key pressures and flows. Right atrial pressure, left atrial pressure, pulmonary artery pressure, and mean aortic pressure are measured with high-fidelity pressure catheters (Millar Instruments, Houston, TX). Flows are measured by transit time ultrasonic flow probes (Transonic Systems, Ithaca, NY) in the pulmonary artery, aorta, coronary artery, and brachiocephalic artery along with assist device flow. The system can be tuned to create the hemodynamic values of a pediatric patient under normal or heart failure conditions. Once tuned to the desired hemodynamic conditions, the loop may be used to test the performance of various circulatory support systems including the intra-aortic balloon pump, left and right ventricular assist devices, or cardiopulmonary support systems such as extracorporeal membrane oxygenation.