Research investigating the association between parents\' physiological reactivity and their ability to self-regulate in parenting contexts typically examines the average physiological response across the duration of a dyadic task, conflating reactivity across a multitude of parent and child behaviors. The present study utilized a moving-window analytical technique to generate a continuous, second x second time series of mothers\' high-frequency heart rate variability (HF-HRV) to conduct an event-based analysis of maternal reactivity in the 10 s following an aversive child event. Analyses examined whether maternal reactivity related to parenting behaviors similarly among maltreating (n = 48) and non-maltreating (n = 29) mother-preschooler dyads. Results indicate that maternal behavior was not associated with average HF-HRV reactivity, but mothers who demonstrated an increase in HF-HRV immediately following a negative child event were more likely to engage in behaviors to return the dyad to a positive state. Findings were specific to incidents of negative child behavior, and results were not moderated by maltreatment status. These results highlight the value of using an event-based design to isolate reactivity in response to targeted events to understand how physiological reactivity supports parenting.