We are inducing the host heart to more efficiently vascularize implanted human cardiac tissue using embedded alginate microspheres to deliver angiogenic growth factors.  Microspheres release VEGF-A, FGF-2, and sonic hedgehog into the local microenvironment after implantation on ischemia/reperfusion injured rat hearts. Vascular perfusion enables detection of patent and efficiently perfused vessels originating from the host. This localized delivery of angiogenic factors from biomaterials within the implanted muscle tissue increased global heart function in ischemia/reperfusion injured rat hearts (Munarin et al 2020). We have also shown that patterned endothelial cell-lined vessels promote early chemotaxis from host vascular populations (Kant et al 2021). Heparin modification of alginate microspheres allows for controlled release of VEGF to improve vascularization (Munarin et al 2021) and or can be utilized with pleiotrophin (PTN), a heparin-binding factor with significant angiogenic activity (Rountree et al 2021).