Studies demonstrating a mnemonic benefit for encoding words in a survival scenario have revived interest in how human memory is shaped by evolutionary pressures. Prior work on the survival-processing advantage has largely examined cognitive factors as potential proximate mechanisms. The current study, by contrast, focused on the role of perceived threat. Guided by the idea that a survival scenario implies threat, we combined measures of heart rate (HR) with affective ratings to probe the potential presence of fear bradycardia as a marker of freezing--a parasympathetically dominated HR deceleration that reflects the initial stage of the defensive engagement. We replicated the mnemonic advantage in behavior and found that the survival scenario was rated higher in perceived negative arousal than a commonly used control scenario. Critically, words encountered in the survival scenario were associated with more extensive HR deceleration, and this effect was directly related to subsequent recall performance. Our findings point to a role for the involvement of neurobiological fear responses in producing the survival processing advantage, as well as potential links between autonomic changes and cognitive processing in adaptive memory.