1. A cardiac monitor for detecting a cardiac event, the monitor comprising: (a) a sensor for sensing an analog signal from a human heart; (b) a device coupled to the sensor, the device having an analog-to-digital circuit system contained therein for digitizing the analog signal to produce a digitized waveform; (c) a processor electrically coupled to the analog-to-digital circuit system, said processor configured to: (i) compute a plurality of values of a heart signal parameter from the digitized waveform, the plurality of values of the heart signal parameter being characterized by a plurality of statistical distributions corresponding to a plurality of heart rates, wherein each statistical distribution is characterized by an upper boundary and a lower boundary and a dispersion; (ii) store data pertaining to the plurality of values of the heart signal parameter in a form that enables characteristics of first and second statistical distributions to be computed for first and second heart rates; (iii) determine first and second boundary values of the heart signal parameter associated with the first and second heart rates respectively; (iv) compute a heart rate dependent detection threshold, wherein the detection threshold is based on the first and second boundary values. (v). apply a test to detect a cardiac event, wherein the test is based on the detection threshold.