The variation of some fundamental constants of nature is a prediction of several unifying theories. As physics at recombination is sensitive to the value of the electron mass and the fine structure constant, cosmic microwave background radiation (CMB) provides an excellent laboratory to constrain such theories. In this work, we used WMAP-3yr data to make a joint estimation of cosmological parameters together with the electron mass and fine structure constant, in order to study what data can tell us about the variation of such constants.