Goldberger, A. L. Is the normal heartbeat chaotic or homeostatic? News Physiol. Sci. 6, 87-91
Limits to the usefulness of homeostasis as a guiding physiological principle are revealed by new mechanisms derived from study of nonlinear systems that generate a type of variability called chaos. Loss of complex physiological variability may occur in certain pathological conditions including heart rate dynamics before sudden death and with aging.