Abstract: Systems and methods are provided for the study of the cardiac rhythm variability. These systems and methods include the recording of the electrocardiogram (EKG), with subsequent calculation of the duration of the beat-to-beat intervals (i.e., R-R intervals), drawing up of the rhythmograms, and additional systems and methods that include determination of, throughout all observation times within particular intervals included in the recording periods, the average values of the informational entropy of the beta-distribution (AE) of the R-R intervals, the differences between the maximum and minimum values of the informational entropy of the beta-distribution (MDE) of the R-R intervals, the root-mean-square deviations of the informational entropy of the beta-distribution (RMSDE) of the R-R intervals, and/or variation factors of the informational entropy of the beta-distribution (VFE) by means of calculation of the informational entropy of the beta-distribution of the R-R intervals.