for a given pacemaker the presence of two or more such intervals one such interval is disregarded is indicative of low rate pacing which results from a discharge of the supply battery of the tested pacemaker below a threshold considered as the limit of the battery 39 s life the 34 normal pacing interval 34 block 128 detects the s to s intervals which are included between the low and high permissible limits as described above each such interval is indicative of a normal pacing rate simultaneously the pacing pulses are tested for their effectivity in stimulation of the heart contractions however for the asynchronous pacer the effectivity test must be preceded by a competition check this is undertaken by the 34 competitive pacing 34 block 129 which is fed from the 34 qrs recognition 34 block 12 fig2 b via the line 110 by a determinant signal simulating the heart retractory period the check is based on sorting out each pacing pulse which is coming within the heart refractory span and excluding it from the effectivity test such a pulse can not be effective in arising a heart contraction by the nature of the heart 39 s response to successive stimulation as described above if among the pacing pulses only one is found to be beyond the heart refractory span this is considered insufficient for drawing out sound conclusions concerning the effectivity of pacing then a signal is fed to the block 122 to signal the necessity of repeating the pacemaker test as described above when two or more pulses are coming beyond the heart refractory span each of them is tested for its effectivity in stimulation of the heart by the 34 effective pacing 34 block 130 this block is fed through the.