Recent years have witnessed an upsurge of research interest in motor imagery (MI; sometimes known as mental practice) or the mental simulation of actions without any concomitant bodily movement. While numerous experimental studies have demonstrated the efficacy of MI in improving skilled performance in fields such as music, sport and medical surgery, few to date have investigated the extent to which MI and motor execution share similar cognitive mechanisms. Therefore, to address this gap, the present studies explored the relationship between the executed and imagined movements of expert pianists. Study 1 explored the effects of movement complexity and force on the time required for nine pianists to actually perform and imagine performing a musical composition. Results revealed that although the durations of participants’ imagined performances were longer than those of executed ones, stage-duration variations during execution were mirrored in the stage-duration variations during MI. In Study 2, seven pianists’ pupil-size measurements (obtained using Tobii eye-tracking glasses) were used to explore changes in cognitive effort between executed and imagined piano performance. Results showed that pupil-size measurements during executed and imagined piano playing were similar. The significance of the findings is discussed and some potential new directions for research are identified.