Genetically engineered light sensitive cardiac cell. The electrophysiology of the cell is characterized in terms of nion = 4 ion concentrations, the intracellular sodium, potassium, and calcium concentrations and the calcium concentration in the sarcoplastic reticulum. Ion concentrations are controlled through ncrt = 16 ionic currents, where we have enhanced the conventional cell model [43, 47] with the channelrhodopsin photocurrent IChR2, here shown in blue [1]. The channels are governed by ngate = 14 gating variables, where we have added the channelrhodopsin gating variable gChR2 to characterize the cell’s response to photostimulation.