Contemporary capacitive discharges are often driven by a combination of at least two frequencies to achieve independent control of the ion flux and the ion energy impacting the electrodes. This multiple frequency excitation leads to new electron heating mechanisms that are discussed in this paper. Firstly, we show that electron heating in the sheath is greatly enhanced by the combination of two frequencies, i.e. the heating produced is much larger than the sum of the two single contributions. Secondly, we show that when the higher frequency is such that the corresponding wavelength becomes comparable to the electrode size, electromagnetic effects become important and a significant amount of heating is provided by the inductive field. The discharge experiences a capacitive-to-inductive transition when the high frequency voltage amplitude is raised.