Two experiments with a total of 96 participants assessed cardiovascular response in active coping. The studies were run in 2x2 designs and manipulated the clarity of task difficulty (clear vs. unclear) and incentive value (low vs. high) of a memory task, which was either easy (Experiment 1) or extremely difficult (Experiment 2). In accordance with the theoretical predictions of motivational intensity theory [Brehm, J.W., Self, E.A., 1989. The intensity of motivation. Annu. Rev. Psychol. 40, 109-131; Wright, R.A., 1996. Brehm's theory of motivation as a model of effort and cardiovascular response. In: Gollwitzer, P.M., Bargh, J.A. (Eds.), The Psychology of Action: Linking Cognition and Motivation to Behaviour, Guilford, New York, pp. 424-453], systolic reactivity varied directly with incentive value when task difficulty was unclear. In contrast, when task difficulty was clear, incentives had no influence and cardiovascular reactivity was low. These findings provide the first evidence for the predictions of motivational intensity theory with regard to unclear task difficulty and complete past research that has focused on the effects of fixed and unfixed task difficulty on cardiovascular reactivity.