Abstract: The amplitude of each R wave of an electrocardiogram signal at each of a plurality of sample points is compared with reference values representing amplitudes of a reference template at the sample points, with each new set of R wave amplitudes at the test points being applied to update the reference values by being averaged therewith. The amplitudes of each R wave which has been determined to differ from the reference template at at least one of the test points are stored in a recirculating shift register memory in addition to being compared to other values previously stored in the memory. Whenever a set of amplitudes is determined to be equal to a set of amplitudes previously stored in the memory, an alarm signal is generated to identify an arrhythmia.