A system analyzes and characterizes cardiac electrophysiological signals by determining instantaneous signal entropy for identifying and characterizing cardiac disorders, differentiating cardiac arrhythmias, determining pathological severity and predicting life-threatening events. A system for heart monitoring, characterization and abnormality detection, includes an acquisition device for acquiring an electrophysiological signal representing a heart beat cycle of a patient heart. A signal processor derives an entropy representative value of the acquired electrophysiological signal within a time period comprising at least a portion of a heart beat cycle of the acquired electrophysiological signal and provides an entropy value as a function of the entropy representative value and the time period. A comparator generates data representing a message for communication to a destination device in response to the entropy value exceeding a predetermined threshold.