Is heart rate variability dynamics poised at criticality?

It is a statement bordering on the obvious that the heart rate regulatory system is a well designed one. Indeed, cardiac dynamics is capable of responding to the broad range of environmental stimuli which we are likely to encounter throughout life. There is a growing evidence that cardiac regulatory dynamics is not unique in the type of the adaptive dynamical characteristics it displays. On the contrary, it appears instead that the parsimonious model of critical behaviour is one which is both deeply rooted in statistical physics and in nonlinear dynamics approaches to complex phenomena. Indeed, it is also identified in a number of biological phenomena, and growing evidence is being gathered, suggesting operational benefits of systems `poised' at criticality.