The mere exposure effect, positive affect elicited by exposure to a previously unfamiliar stimulus, is considered one of the most well established findings in the psychological literature. Yet its mechanism remains unknown. In Experiments 1 - 5, memory encoding was examined to determine whether the mere exposure effect was a form of conceptual or perceptual implicit priming, and, if not either, whether cardiovascular psychophysiology could reveal its nature. Experiment 1 examined the effects of study phase level of processing on recognition, the mere exposure effect, and word identification implicit priming. Deep relative to shallow processing improved recognition, but did not influence the mere exposure effect or word identification implicit priming. Experiments 2 and 3 examined the effect of study-test changes in font and orientation, respectively, on the mere exposure effect and word identification implicit priming. Different study-test font and orientation reduced word identification implicit priming, but had no influence on the mere exposure effect. The combined results from Experiments 1-3 suggested that conceptual and perceptual processing do not drive the mere exposure effect. Experiments 4 and 5 developed and used, respectively, an innovative cardiovascular psychophysiological implicit priming paradigm to examine whether stimulus-specific cardiovascular reactivity at study predicted the mere exposure effect at test. At encoding, stimulus-specific peripheral vasodilatation had predictive value for the mere exposure effect, but not for word identification implicit priming. Experiments 6 and 7 examined whether sustained or transitory anxiety (i.e., trait or state, respectively) would influence the mere exposure effect. Greater trait and state anxiety reduced the mere exposure effect. Together, the findings from these experiments (N = 362) identify a novel affective mechanism of implicit priming that is influenced by cardiovascular psychophysiology and variations in trait and state anxiety.