Electrocardiograms of 65 patients treated with dothiepin, a sulphur substituted tricyclic antidepressant, were compared to those of 57 patients receiving amitriptyline and 62 patients given placebo. Amitriptyline produced an average heart rate increase of 10 beats/minute as compared to 5 beats/minute for dothiepin (p less than .02). Amitriptyline also produced a significant prolongation of the corrected QT interval as compared to both dothiepin and placebo (p less than .01 and p less than .001, respectively). Dothiepin had no significant effect on any index of myocardial conduction (PR interval, corrected QT interval, and QRS duration) as compared to placebo.