The invention is a method for estimating a cardiac frequency via the detection of radiation backscattered or transmitted by a bodily zone. The part is illuminated, simultaneously or successively, by light radiation extending over a first spectral band and a second spectral band. A photodetector detects radiation emitted by the bodily zone under the effect of its illumination, in each of the spectral bands. A first detection function and a second detection function are formed from the radiation detected in each spectral band, respectively. The method allows the cardiac frequency to be determined via the determination of characteristic instants that are identified from the first detection function and the second detection function simultaneously.