Extensive investigation of electron heat transport mechanisms by means of heat wave propagation techniques has been carried out in JET plasmas. Electron temperature (Te) modulation experiments were made possible by exploiting the direct, localized and tunable electron power source provided by mode conversion of the launched ICH power to short wavelength waves at the ion-ion hybrid layer. In addition, cold pulses from the edge have been launched using Ni laser ablation or shallow pellets. The experiments have been carried out in L- and H-mode plasmas in order to explore the issue of stiffness in the elec-tron channel, and in plasmas with Internal Transport Barriers (ITB) in order to probe the transport in the ITB layer. Theoretical modelling of the results using empirical models and turbulence simulations has been performed. In particular, the use of an empirical model based on a criti-cal temperature gradient length has allowed quantification of stiffness and comparison between stiffness in different machines.