Styryl voltage sensitive dyes (e.g. di-4-ANEPPS) have been widely and successfully used as probes for mapping membrane potential changes in cardiac cells and tissues. However, their utility has been somewhat limited because their excitation wavelengths have been restricted to the 450-550nm range. Longer excitation/emission wavelength probes can minimize interference from endogenous chromophores and, because of decreased light scattering and lower absorption by endogenous chromophores, improve recording from deeper tissue layers. In this paper we report on our efforts to develop new potentiometric styryl dyes that have excitation wavelengths ranging above 700nm and emission spectra extending to 900nm. Three dyes for cardiac optical mapping were investigated in depth from several hundred dyes containing 47 variants of the styryl chromophores. Absorbance and emission spectra in ethanol and multi-lamellar vesicles (MLV), as well as voltage-dependent spectral changes in a model lipid bilayer have been recorded for these dyes. Optical action potentials were recorded in typical cardiac tissues (rat, guinea pig, pig) and compared to that of di-4-ANEPPS. The voltage sensitivities of the fluorescence of these new potentiometric indicators are as good as those of the widely used ANEP series of probes. In addition, due to molecular engineering of the chromophore the new dyes provide a wide range of dye loading and washout time constants. These dyes will enable a series of new experiments requiring the optical probing of thick and/or blood perfused cardiac tissues.