Fast, transient cardiac accelerations and decelerations during fear conditioning in rats

► Rats were fear conditioned to a series of six auditory pips that predicted a shock. ► A small transient heart rate deceleration occurred to each pip in the series. ► Each deceleration was followed by a brief phasic acceleration. ► These fast responses were nested in a slow increase in heart rate across all pips. ► We argue that these fast responses are similar to evoked cardiac responses in humans.