Figure 1. Schematic diagram of a typical optical mapping system. The preparation is stained with a voltage-sensitive dye. The optics, which can include single or tandem photographic lenses, microscope objectives, or fibre optics, focus the fluoresced light onto the photodetector. The photodetector can be either a photodiode array or a CCD camera.

Figure 2. Conceptual representation of electrochromic dye molecules (such as di-4-ANEPPS) bound to the cell membrane. The dye responds directly to the membrane's electric field and senses the local values of membrane potential on the time scale of nanoseconds. Absorption of photons by the dye molecule excite it to a higher energy state and causes the emission of a photon of a longer wavelength.

Figure 3. The mechanism of voltage-sensitive fluorescence in an electrochromic dye. A change in transmembrane potential causes the fluorescence emission spectrum to shift. The spectral shift alters the magnitude of fluorescent light that is passed by a longpass filter (shaded region). Di-4-ANEPPS, for example, exhibits a fluorescence intensity change that varies linearly with membrane potential.

Figure 4. (a) Optical action potentials from selected sites across the ventricular epicardial surface of a cannulated and perfused guinea-pig heart. Depolarization times are assigned at the point of most rapid rise of the action potential upstroke. (b) The activation sequence is determined from a relative timing of local depolarizations measured at each of hundreds of recording sites across the surface of the heart.