Purpose: To examine whether electrical stimulation of the masseter muscle triggered by heart rate elevation preceding sleep bruxism (SB) can actively suppress SB. Materials and Methods: Ten volunteers who were aware of their SB habits participated in the study. Baseline electromyogram (EMG) activity of the unilateral masseter muscle and electrocardiogram (ECG) signal were recorded on the first night. The individual mean sensation and pain thresholds to electrical stimulation of the unilateral masseter muscle were determined in awake subjects before the experiment. On the second night, electrical stimulations at either of the two threshold intensities were automatically generated and delivered to the masseter muscle on the opposite side from where electrodes were placed immediately after the heart rate exceeded 110%. On the third night, electrical stimulations at the other threshold intensity were delivered. Results: The numbers of SB events per night and per hour, the number of EMG bursts per SB event, and the duration of SB events decreased significantly on the nights when stimulation was applied compared with the baseline data. There were no significant differences between cases where the sensation threshold was used as the stimulation intensity and those in which the pain threshold was used as the stimulation intensity. Conclusion: The results suggest that electrical stimulation of the masseter muscle triggered by heart rate elevation can significantly suppress SB. Int J Prosthodont 2014;27:80-86. doi: 10.11607/ijp.3330