Pain is the most common symptom reported by breast cancer survivors (BCS), and it significantly affects their quality of life. Higher vagally mediated heart rate variability (vmHRV) is associated with higher emotional awareness (EA) and lower pain. This study examines the moderating role of vmHRV in the association between EA and pain among BCS, which, to our knowledge, has not previously been explored. The study is a cross-sectional secondary analysis of baseline data from an existing study exploring mental health outcomes after art therapy. Participants were 156 female BCS 14 months after cancer diagnosis. We measured vmHRV indexed by the root mean square of successive differences (RMSSD) at rest via electrocardiogram recordings, levels of EA via a performance measure, and how much pain interferes with daily life activities and the intensity of pain in one's daily activities through questionnaires. A negative association was found between RMSSD and pain intensity but not pain interference or EA. At high but not low RMSSD, EA was negatively associated with pain intensity. High EA supports implicit-to-explicit emotional processing, increased vmHRV supports top-down modulation of the nervous system, and both are relevant to pain. Further research is needed to explore the impacts of EA and vmHRV on pain management and psychotherapy interventions.