Objectives. We tested the hypothesis that aging is associated with an increase in the effort and costs associated with cognitive activity using systolic blood pressure (SBP) as a measure of effort. Method. Younger and older adults engaged in an initial task (Phase 1) for 5 min that was relatively low (adding single digits) or high (subtracting by 3 s) in cognitive demands. They then solved a series of multiplication problems for 3 min (Phase 2). Cardiovascular measures were collected throughout, and reactivity was examined as a function of age, initial task difficulty, and test phase. Results. Older adults exhibited higher levels of reactivity than younger adults to cognitive engagement, with reactivity increasing with task difficulty. Difficulty of the initial task was also associated with greater effort and lower performance on the subsequent multiplication task, suggestive of fatigue or depletion. These fatigue effects were stronger for older adults. Discussion. The results were consistent with expectations and provided support for the utility of SBP reactivity as a measure of cognitive effort in studies of aging.