Patrick M. Boyle et al. JACEP 2018;4:155-167 Mechanistic Studies of Arrhythmia Dynamics Enabled by Optogenetics (A) Activation maps showing spiral wave chirality reversal in response to patterned optogenetic stimuli applied sequentially. (B, C) Activation maps showing stable rotors with region of illumination (blue) superimposed (left). Optically mapped voltage traces recording before, during, and after illumination (right); black and blue square-wave plots show timing of electrical and optogenetic stimuli, respectively. Patrick M. Boyle et al. JACEP 2018;4:155-167 2018 American College of Cardiology Foundation