A variable rate cardiac pacemaker is adapted to be implanted in a human patient for automatically adapting pacing rate to metabolic need of the patient when the patient is walking in an ascending path, a descending path, or on a level plane. An accelerometer senses the activity of the patient walking, and produces an electrical sensor signal representative of the activity. The accelerometer signal has variable parameters indicative of morphology, including amplitude, of the sensor signal according to status of activity of the patient and to the upward, downward, or horizontal direction of the patient's walking. A pulse generator generates pacing pulses at a variable rate according to an applied control signal to electrically stimulate the patient's heart at a pacing rate which varies according to patient activity. A processing and control circuit of the pacemaker processes the sensor signal for detecting differences in the signal morphology attributable to whether the patient is walking on an ascending path, a descending path, or a level path, irrespective of the presence or absence of disparity in the amplitude of the sensor signal resulting from walking along the respective path. The latter circuit also develops the control signal to dictate a basic pacing rate from the amplitude of the sensor signal, and an enhanced rate more appropriate to the metabolic need of the patient from the detected differences in morphology of the sensor signal, for application to the pulse generator.