This 2-week-old heart organoid — with cardiomyocytes (green) and smooth muscle cells (white) — is surrounded by endothelial cells (magenta) that form a network of realistic blood vessels.

This 2-week-old heart organoid — with cardiomyocytes (green) and smooth muscle cells (white) — is surrounded by endothelial cells (magenta) that form a network of realistic blood vessels.