Circulatory physiology in the developing embryo.

Knowledge of early developmental circulatory physiology has lagged behind advances in molecular cardiology. Cardiovascular physiology changes during embryonic development in a highly complex and carefully orchestrated manner, tightly correlated with structural development. Circulatory changes in early development include increasing heart rate, preload, and cardiac output; decreasing peripheral resistance; and increasing ventricular compliance, paralleling the increasing metabolic needs of the growing embryo. Newer techniques and the recent ability to study mammalian models of development have led to further insight into changes in myocardial and peripheral vascular physiology. The next major challenges include understanding the mechanisms regulating cardiovascular hemodynamics, normal physiologic adaptation of the growing embryo, and the physiology of abnormal cardiovascular development.