It's about effort: Impact of implicit affect on cardiovascular response is context dependent.

Based on the Implicit-Affect-Primes-Effort model, we tested whether the effect of implicitly processed affect primes on cardiovascular responses is limited to settings that call for effort and in which implicit affect can inform about subjective task demand. Participants were presented with letter series and briefly flashed sadness versus happiness primes. Half of the participants were asked to memorize all occurring vowels (achievement context), while the other half merely watched the series (watching context). Responses of cardiac pre-ejection period, heart rate, and systolic and diastolic blood pressure supported the predictions. As expected, in the challenging achievement-context condition, happiness primes led to stronger cardiovascular reactivity than sadness primes. By contrast, reactivity was modest in both affect prime conditions when the participants merely watched the stimuli. That is, the impact of affect primes on cardiovascular responses was limited to a setting that directly called for effort mobilization.