This study presents an attempt to extend the knowledge of autonomic factors in emotion by studying the cardiac behavior of cats in emotional situations. Action potentials of the heart beat were amplified and recorded on ticker tape by means of an undulator. Stimuli consisted primarily of pistol shots and the presentation of dogs. A shot elicits an acceleration of heart beat, with a latency of .54 sec. on the average. The action time varies, according to the magnitude of the response, from .42 to 2.3 sec. The recovery time also depends upon the magnitude of the response, but shows an average duration of 4 sec. The extent of the rise in heart rate is about 30 beats per minute. Sudden presentation of a menacing dog produces a marked change in heart rate. For the first two presentations to two cats the average rise was 81% of the base rate. In this rise there is usually a sharp peak in heart rate within .35 to 1.25 sec. of stimulation. The temporal features of the startle response to shots and the rapidity of occurrence of the sharp peak in the response to dogs may be compared to the temporal features of cardiac response to direct stimulation of autonomic nerves. The comparison suggests that the sudden response to shots and dogs must be due to the activity of the parasympathetic system. (PsycINFO Database Record (c) 2012 APA, all rights reserved)