Explicit personality tests assess introspectively accessible self-descriptions. By contrast, implicit personality tests assess introspectively inaccessible processes that operate outside of awareness. Despite their inaccessibility, implicit processes are presumed to influence a variety of current responses. This study tested the hypothesis that an implicit anxiety test should predict cardiovascular reactivity during a speech stressor task. In all, 97 participants completed a measure of attention allocation toward threat (implicit test) and an anxiety questionnaire (explicit test) 1 week before giving an evaluated speech. Whereas the explicit test showed modest relations within only 1 measure of cardiovascular reactivity, the implicit test predicted heart rate and blood pressure reactivity during preparation and delivery of the speech. These findings encourage the broader use of implicit measures to assess cardiovascular responses to threat.