The cardiovascular system is composed of a variety of specialized subsystems that interact with each other under the influence of internal and external inputs, including central commands, reflex mechanisms, and humoral factors. The concomitant action of all these subsystems produces continuous adjustments in the cardiovascular variables (e.g., heart rate, heart contractility, blood pressure, vascular tone, etc.) referred to as cardiovascular variability. A large body of evidence indicates that this variability includes linear and nonlinear components and conveys important biological information that might help in the understanding of the underlying physiology and facilitate diagnosis and prognosis of cardiovascular dysfunctions.