Fast and controllable surface acoustic wave (SAW) driven digital microfluidic temperature changes are demonstrated. Within typical operating conditions, the direct acoustic heating effect is shown to lead to a maximum temperature increase of about 10 degrees C in microliter water droplets. The importance of decoupling droplets from other on-chip heating sources is demonstrated. Acoustic-heating-driven temperature changes reach a highly stable steady-state value in approximate to 3 s, which is an order of magnitude faster than previously published. This rise time can even be reduced to approximate to 150 ms by suitably tailoring the applied SAW-power excitation profile. Moreover, this fast heating mechanism can lead to significantly higher temperature changes (over 40 degrees C) with higher viscosity fluids and can be of much interest for on-chip control of biological and/or chemical reactions.