Behaviorally elicited cardiac arrests have been observed in different phyla independently of the neurogenicity or myogenicity of pacemakers. Startling stimuli such as visual detection of close and fast movement is especially associated with complete cardiac inhibition. In contrast, orienting responses are associated with bradycardia. Although studies on vertebrates are not usually concerned with reflex responses, it can be assumed that actual cardiac arrests occur in some cases in which bradycardia is reported, but that these arrests cannot be recorded because of the methodology used. Heart rate can be used to separate patterns displayed in such defensive reflex behaviors as orientation, startle, and freezing. Behavioral sequences can be categorized into various series of patterns which correspond to various sequential and multiphasic heart-rate patterns. © 1982, Psychonomic Society, Inc.. All rights reserved.