Every beat of your heart is tightly controlled by special pacemaker cells that emit waves of electrical signals across your heart. These signals raise calcium levels in heart cells, causing them to contract. With limits in microscopy, studying this has often involved removing the heart from an animal. Researchers now use zebrafish to study this in vivo using live 3D imaging. Zebrafish were genetically altered to express a dye in their heart cells that fluoresces when calcium levels rise. The team imaged and modelled the changing shape of the developing zebrafish heart (pictured, clockwise from top left) over the course of 300 milliseconds (pink, purple, blue, green, yellow and orange corresponding to 50 millisecond chunks of time). The rising calcium levels spread across the heart at different speeds according to differences in its anatomy. This approach allows the simultaneous study of whole organ and cell level changes during heart development.
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