Autonomic Effects in the Developing Heart

Embryonic and fetal hearts have been studied for over 300 yr. Initially, the effects on the rate of impulse generation of various physical factors (e.g., temperature) and chemicals were observed. Later, cardiac electrophysiologic properties, including the characteristics of transmembrane action potentials, were investigated. Changes related to age and development were observed in these studies, the vast majority of which utilized the chick embryo and, to a lesser extent, the rat embryo. Although the heart of the human embryo or fetus has been studied, it has not been possible to perform detailed electrophysiological studies over the entire gestational period.