Optical mapping has become a powerful tool to explore complex cardiac propagation. Many experiments and studies claimed that the fluorescence obtained from tissue surface is the averaged response of the transmembrane potential upon probing depth rather than only on the surface. With the electrical propagation model and the photon transport model, the effects of depth-weighted optical signals are examined both during a normal excitation wave and a spiral wave. Our results indicate that depth-weighted optical signals may infer cardiac activation dynamics, such as the mode and the direction of the propagation, the spatial distribution of depolarization or repolarization.