Abstract Body: Heart regeneration by remuscularization after myocardial infarction (MI) uses human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to restore cellular and functional loss. The approach of implanting engineered human myocardium (EHM), composed primarily of CMs in a collagen hydrogel, has already moved into clinical trials. However, these tissues are soft with disorganized sarcomeres and require mechanical support from extraneous non-degradable biomaterials to be surgically handled. To create a robust implant that reinforces the EHM and also the heart, we incorporate a biodegradable polycaprolactone (PCL) scaffold in our EHM to initially stabilize the injured heart and degrade as CMs mature and healing resolves. This study investigates how PCL degradation impacts scaffold mechanics and macrophage polarization and develops a novel 3D PCL architecture to mechanically reinforce the heart while enhancing EHM-PCL entwinement, CM organization, tissue bundle formation, and contractility. Degradation results show stable mechanical properties over one month in vitro, suggesting an ability of the PCL scaffold to support the EHM during culture and post implantation. Architected fibrous PCL scaffolds formed by melt electrowriting (MEW) exhibit anisotropic mechanical properties, meaning that upon implantation, it will be stiffer along the heart’s longitudinal direction for infarct stabilization and softer in the circumferential direction for diastolic compliance. MEW creates reproducible PCL scaffolds with aligned fibers (diameteres: 0.6-36.7μm) with tunable stiffnesses (20.9 kPa-7.69 MPa) and anisotropy (longitudinal/transverse ratio: 8-317). These scaffolds are integrated in a PCL-EHM composite to instruct CM morphology and add mechanical robustness for surgical handling. Our ongoing work refines the scaffold design for optimal mechanical properties and EHM integration; assesses the composite’s CM alignment and contractility; and evaluates macrophage response to PCL degradation. This new approach will enable the delivery of strongly contractile and aligned CMs in EHM with tunable, biodegradable mechanical support for the heart as an early intervention to remuscularize and unload the post-MI heart.