heart rate reactivity
changes in heart rate associated with particular emotional states. It is usually held that heart rate increases in states of fear, anger, and scorn and decreases in states of attentiveness, positive emotional reaction, and interest. However, the actual relation between heart rate and emotion is complex and largely mediated by the energy demands of the bodily musculature of the organism in an emotional state. Thus, a frightened animal that reacts with tonic immobility (death feigning) and limpness will show a reduction in heart rate in its reaction to a threat, whereas an animal that is immobile but poised for flight typically shows acceleration of heart rate. States of laughter, although pleasurable, are typically associated with an accelerated heart rate owing to the involvement of large muscle groups in the act of laughing.