ABSTRACT Cardiac muscle generated from human induced pluripotent stem cells (iPSCs) is being increasingly used to model heart injury and regeneration. The lack of maturity, multicellular composition, perfusable vasculature and patient specificity remain the key limitations of currently available cardiac tissue models. Several advances, achieved in our labs during the previous grant cycle, form the basis for the proposed patient specific studies of viral myocarditis and ischemia- reperfusion injury: (i) Derivation of multiple cell types that compose native myocardium (cardiac myocytes, cardiac fibroblasts, endothelial cells, mesenchymal stromal cells, circulating and resident macrophages), all from the same starting human iPSCs for biological complexity and patient specificity. (ii) Perfusable microvascular networks serving as a template for engineering vascularized cardiac muscle. (iii) Ability to link tissues by vascular perfusion in a way allowing the maintenance of the individual tissue niches while enabling cross-talk by circulating cells, extracellular vesicles (EVs) and secreted factors. (iv) Development of an isogenic model of bone marrow, serving as a source of immune cells when linked to the cardiac muscle by vascular flow. (v) Models of viral myocarditis and ischemia-reperfusion injury, with data indicating the sex specificity and therapeutic effects of EVs. We propose to build upon these advances and bioengineer patient-specific vascularized human cardiac microbundles to study the individual differences under normal conditions, and following the viral myocarditis, ischemic injury and EV treatment. We hypothesize that the vascularized cardiac muscle of such a high maturity and biological fidelity will be able to capture sex-specific responses to cardiac injury. To test this hypothesis, we propose three specific aims that will be pursued in an integrated fashion, with the outcomes of each aim informing the other two aims. Aim 1 is to engineer multicellular, patient- specific, vascularized cardiac microbundles. Aim 2 is to deploy vascularized cardiac microbundles in modeling acute viral myocarditis, for which males are at a higher risk. Aim 3 is to deploy vascularized cardiac microbundles in modeling acute and sustained ischemia-reperfusion injury, with females are at a higher risk. For both Aim 2 and Aim 3, we will also study the cell-protective measures of EVs and miRNAs in their cargo. We believe that this work will have impact on both the biological research and the treatment of heart injury and disease.