In the last decade the role of structural dynamics in controlling protein function was actively investigated using new and advanced experimental approaches. In particular, time resolved crystallography, despite some practical difficulties, is being used extensively to complement the study of protein structure-function relationships with information on the dynamics, based on experimental evidence. Here we present a short overview of the results obtained on dynamical properties of myoglobin and homologous hemoproteins, where the photosensitive heme-Fe--ligand bond has allowed transient intermediates to be studied by different flash photolysis methods coupled to Laue X-ray diffraction, thus highlighting some of the dynamical events that characterize diffusion of a diatomic ligand to/from the heme in model hemoproteins.