Another system that exhibits multifractal behaviour, is the heart rate variability, (HRV). HRV was studied by a variety of multifractal approaches, such as the Detrended Fluctuation Analysis, the Average Wavelet Coefficient Analysis and the Entropy in Natural Time Analysis. Papasimakis, N. and Pallikari, F. (2010) Correlated and uncorrelated heart rate fluctuations during relaxing visualization. EPL 90 48003