(A) Stacking five single EHTs (B) on a custom-made device facilitated EHT fusion and allowed contractions under auxotonic load resulting in synchronously contracting (C) multiloop EHTs ready for in vivo engraftment. (D) Six single-knot sutures served to fix multiloop EHTs on (E) the recipient hearts ((A-E), with permission from [] ). (F) Photograph of an assembled electrical stimulation chamber developed by Radisic and colleagues for applying pulsatile electrical field stimuli to (G) cardiac cells seeded on scaffolds. (H) Representative transmission electron micrographs of stimulated and non-stimulated constructs after 8 days of cultivation, compared with neonatal rat ventricles. (I) Stimulated constructs and neonatal ventricles contained higher levels of β-Myosin heavy chain staining compared to non-stimulated constructs ((F-I), with permission from []). (J) Decellularized cadaveric rat heart. (K) H&E staining indicates no intact cells or nuclei with large vascular conduits maintained (black asterisks) Scale bar, 200 μm. (L) Immunofluorescence staining of cadaveric and SDS-decellularized rat heart thin sections showing the presence or absence, respectively, of DAPI-positive nuclei (purple), cardiac α-myosin heavy chain (green) and sarcomeric α-actin (red). Scale bars, 50 μm. (M) Recellularized whole rat heart at day 4 of perfusion culture, showing cross-sectional ring harvested for functional analysis (day 8, Upper Insert), and Masson’s trichrome staining of a ring thin section showing cells throughout the thickness of the wall (Lower Insert). Scale bar, 100 μm. Force generation in recellularized left ventricular rings after (N) 1-Hz and (O) 2-Hz electrical stimulation ((J-O), with permission from []).