From the spontaneous sequence method, a new index of baroreceptor function has recently been proposed, the baroreflex effectiveness index (BEI). BEI quantifies the number of times the baroreflex is effective in driving the sinus node. In this study we examined how different cognitive-attentional demands modulates BEI and baroreceptor reflex sensitivity (BRS). Eighty three students performed three tasks: mental arithmetic, memory, and visual attention. Results indicate that BRS reliably decreases during mental arithmetic and increases slightly during visual attention. BEI increases during the visual attention task. The overall pressure change of the systolic blood pressure ramps decreases during tasks with respect to baseline periods and cannot explain the effect found in BEI (in effect, BEI works against this underlining influence). The modulation found in BRS and BEI as a function of cognitive demand is in accordance with the Laceys' intake/rejection theory. Specifically, it is suggested that BRS is more sensitive to internal cognitive elaboration conditions, while BEI is more sensitive to external attention conditions.