A variable rate cardiac pacemaker having an accelerometer for setting a pacing rate characterized by a ratioing circuit for determining a ratio of positive accelerations to negative accelerations and setting the pacing rate in response to the ratio. The ratio may be determined from the duration of the accelerometer signal above and below a reference, or from an integration of that value. The reference may be electrical zero or some other value such as a rolling average. The positive and negative accelerations may be weighted to favor response to either positive or negative accelerations. The integrated values may also be squared or otherwise enhanced by a factor to increase responsiveness.