Fig. 3: hHO cardiac cell lineage composition.

a–e Immunofluorescence images of various cell lineages composing the hHOs. a, Cardiac fibroblast markers THY1 (green) and VIMENTIN (white) present throughout the hHOs, TNNT2 (red), DAPI (blue); scale bar: 500 µm, inset: 50 µm. b Endocardial marker NFATC1 (green) highly expressed within chambers of TNNT2 ⁺tissue (red); scale bar: 500 µm, inset: 50 µm. c–e Endothelial marker PECAM1 (green) showing a defined network of vessels throughout the organoid and adjacent to TNNT2 ⁺ tissue (red), DAPI (blue); showing a single confocal plane (c), a maximum intensity projection to visualize the vascular network throughout the organoid (d), and a high magnification 3D reconstruction showing tubular endothelial structures (e); red dotted circle in (d) indicates area of high vascular branching. Scale bar: c, d: 500 µm, e 50 µm. f Pie chart of average cell composition in hHOs, calculated as the percentage of cells with respective cell marker over all cells by nuclei counting using ImageJ. g Sketch of hHO surface (top) and cross-section (bottom) showing the organization of cell types and features of the hHOs. Source data are provided as a Source Data file.