A system for heart performance characterization and abnormality detection comprises an input processor and a signal processor. The input processor receives first sampled data representing a first signal portion of a heart activity related signal and second sampled data representing a second signal portion of a heart activity related signal. The signal processor determines distribution data associated with degree of similarity between the first and second signal portions by determining a difference between (a) values derived by applying a first function to mean adjusted sampled values of the first signal portion and (b) values derived by applying a second function to mean adjusted sampled values of the second signal portion. In response to the determined distribution data, the signal processor initiates generation of a message associated with the degree of similarity between the first and second signal portions.