“…However, since human heartbeat is essentially nonstationary and highly complex the nonlinear HRV techniques derived from mathematics of complex dynamics fractal geometry have been proven to be superior in clarifying changes of autonomic activity in coronary artery disease, rhythm disturbances, heart failure or following myocardial infarction and in independently predicting benign and malignant arrhythmias, sudden cardiac death and mortality after myocardial infarction [4,[26][27][28][29][30]. Furthermore, applying selected nonlinear HRV techniques in our earlier studies we have confirmed that a profound derangement of sympathovagal balance occurs not only as a result of underlying disease but also as a consequence of a surgical procedure be it with or without the utilization of extracorporeal circulation [14,15]. In the last decade it became evident that human heartbeat belongs to a special class of multifractal bio-signals displaying such an extraordinary complexity and self-similarity over multiple time and space scales that it cannot be indexed by a single global exponent [7,8].…”