Conceptualizations of parasympathetic and sympathetic activity of the autonomic nervous system as representing a bi-dimensional autonomic space have driven recent discussions surrounding the degree of respective and interactive influence of each branch on visceral organs (e.g. heart). An important consideration of autonomic influences on cardiac function is the presence of at least three types of functions: chronotropy, inotropy and dromotropy, each of which shares a unique relationship with ANS activation including sympathetic-parasympathetic interactions. Additionally, the heart is composed of a number of types of effector tissues such that the influence of ANS activation at the sinoatrial (SA) node differs from that at the atrioventricular (AV) node, and these effector sites may reflect sympathetic contributions to the interactive ANS dynamic even under tonic conditions. Given recent indications that tonic cardiac parasympathetic influences appear to vary significantly as a function of ethnicity, it is not yet known to what extent this difference may extend to sympathetic cardiac influences or the degree to which the modes of interaction between the PNS and SNS may be affected. The present investigation sought to further delineate the respective and interactive contributions of parasympathetic and sympathetic influences on the heart, and to explore the influence of individual differences on these measures.