-Computational entropies are methods of non-linear analysis that allows an estimate of the irregularity of a system. Different types of computational entropy were considered and tested in order to obtain one that would give an index of signal complexity taking into account the size of the analysed time series, the computational resources demanded by the method, and the accuracy of the calculation. An algorithm for the generation of fractal time-series with a certain value of the spectral exponent β was used for the characterization of the different entropy algorithms. We obtained a significant variation for most of the algorithms in terms of the series size, which could result counterproductive for the study of real signals of different lengths. The best method was sample entropy, which shows great independence of the series size. With this method, time series of heart interbeat RR intervals or tachograms of healthy subjects and patients with congestive heart failure were analysed. The calculation of sample entropy was carried out for 24-hour tachograms and time subseries of 6-hours for sleepiness and wakefulness. The comparison between the two populations shows a significant difference that is accentuated when the patient is sleeping.