Photosensitive cardiac rhythm modulation structures and systems are described. A genetically-engineered tissue comprising a population of pacing cells expressing a photosensitive membrane transport mechanism that is responsive to light of a particular wavelength(s) combined with one or more of a light source, a power generator, and a sensor provides pacemaker and/or defibrillator function to a subject. The systems further provide in vitro model systems for electrophysiological studies.
