  In nature, excitable reaction-diffusion systems found in diverse settings
(e.g. chemical reactions, metal rust, yeast, amoeba, heart, brain) generate
geometrically similar macroscopic waves(1,2). For the heart and brain, the
spatiotemporal patterns formed by these excitation waves separate healthy from
diseased states(1-3). Current electrical and pharmacological therapies for
bioelectric disorders often lack the necessary spatiotemporal precision needed
to control these patterns. Optical methodologies have the potential to overcome
these limitations, but have only been demonstrated in simple systems, e.g. the
Belousov-Zhabotinsky (BZ) chemical reaction4. Here we combine novel dye-free
optical imaging with optogenetic actuation for dynamic control of cardiac
excitation waves. We leverage patterned light to optically control emergent
macroscopic properties of cardiac tissue: wave direction, wave speed, and
spiral wave chirality. This all-optical approach offers a fundamentally new
experimental platform for the study and control of pattern formation in complex
biological excitable systems.
