Abstract: An implantable heart-monitoring device designed to distinguish two differing heart rhythms. The device comprises electrodes, a template, and first, second and third electronic mechanisms. The first electronic mechanism converts electrical representations of heartbeats from the electrodes into digital data and performs calculations including at least a partial discrete wavelet transform upon the digital data to generate a subset of discrete wavelet transform components including components for distinguishing the two differing heart rhythms and also demonstrated to be relatively low in variability from one patient to another. The template contains a corresponding subset of discrete wavelet transform components captured from at least one individual whose heart was beating in accordance with one of the two differing heart rhythms. The second electronic mechanism correlates the subset of transform components against the template components and provides a correlation value.