This study examines cardiovascular responses indicating challenge (vs. threat) during motivated performance of women under social identity threat. Low gender identified women should primarily be concerned with their personal identity and self-worth, leading them to benefit from self-affirmation under social identity threat. Highly identified women, conversely, should care more for the value of their group and benefit more from group affirmation. Among 64 female participants social identity threat was induced by emphasizing gender differences in car-parking ability. Then, participants received an opportunity to affirm the self or the group and worked on a car-parking task. During this task, cardiovascular challenge versus threat responses were assessed according to the biopsychosocial model (Blascovich, 2008). Results confirmed predictions by showing that self-affirmation elicited cardiovascular patterns indicating challenge in low identifiers, while group affirmation elicited challenge in high identifiers. Theoretical implications for work on social identity are discussed.