Congenital heart diseases are the most frequently diagnosed birth defect of the cardiovascular system (CVS), occurring in 1% of live births globally. Mock circulatory loops (MCLs) replicate the physiological boundary conditions of the CVS, which allow for testing of cardiac assist devices (CADs), but also provide valuable in vitro data for optimizing imaging protocols as well as validating computational fluid dynamics simulations. However, innate limitations of traditional MCLs include the difficulty in tuning physical boundary conditions to match the dynamic patient’s physiology. To address these limitations, hybrid mock circulatory loops (HMCLs) incorporate elements of both in vitro and in silico modelling allowing for rapid changes in boundary conditions to be mimicked in closed-loop. In this study, a real-time HMCL testing platform was built, and its use exemplified in the study of aortic coarctation (AoC), a common congenital cardiovascular disorder caused by a narrowing of the descending aorta. Compliant 3D-printed stenosed tubes of varying severity were integrated into the HMCL to represent the AoC model. First their mechanical impedance was quantified using a chirp pressure signal. Second, the effect of the severity of coarctation on the simulated CVS variables (pressure difference, cardiac output) was assessed in dynamic interaction with the closed-loop CVS. This study lays the foundation for future studies into dynamic cardiovascular conditions, imaging improvements, and validation of fluid dynamics modelling.