A rate-responsive cardiac pacemaker in which deceleration of the pacing rate is modulated according to recent patient activity or "work". Based on signals provided from an activity sensor in the pacemaker, the pacemaker maintains and periodically recomputes a work value corresponding to the amount of patient activity detected over time. In response to a decrease in or cessation of detected patient activity, the pacemaker reduces the pacing rate, first at a more rapid deceleration rate, then at a lower deceleration rate, and then once again at a more rapid deceleration rate. The length of time during which the pacing rate is reduced at the lower deceleration rate is modulated according to the work value maintained by the pacemaker. The work-modulated pacing rate deceleration occurs only if certain achievement criteria are met, the achievement criteria being specified in terms of the amount of time the pacemaker's target pacing rate exceeds a predetermines rest value, and the difference between the target rate and the rest rate.