Peritraumatic dissociation (PD) is one of the best predictors of posttraumatic stress disorder (PTSD). In this pilot study, we examined cardiovascular psychophysiology and negative emotions in 19 adults who, retrospectively, reported experiencing high or low levels of PD during the worst trauma of their lives. In a contiguous series of ten-minute phases, they rested, thought about, talked about, and recovered from talking about their index trauma. We hypothesized that greater PD would be associated with more negative emotion, lower cardiovascular activity, and greater discordance between negative emotions and cardiovascular activity. Our main findings were that PD was associated with lower blood pressure prior to talking about the trauma, greater negative emotion while talking about the trauma, and greater emotional and cardiovascular discordance throughout the experiment. These findings add to the very limited empirical data on physiological concomitants of peritraumatic dissociation and may aid in developing preventive interventions for PTSD.