"This paper deals with changes in heart-rate induced in man by pistol shots." The increment in heart-rate is specified in terms of the index of cardiac startle, i.e., the difference between the peak rate in the 5 seconds following the stimulus and the average rate for the 12 seconds preceding the stimulus. "The startle response becomes habituated by successive shots, but the response may be disinhibited by the interpolation of either a different stimulus or a lapse of time. There is some indication that the increment in heart-rate is positively correlated with subjective report of startle and with skeletal movement. The repeat-reliability of the index of cardiac startle on thirty-three subjects was .53 ± .08 . . . The neural mechanism responsible for the increment in heart-rate is the release of vagal inhibition of the heart and not an increase in sympathetic activity." (PsycINFO Database Record (c) 2006 APA, all rights reserved)