A KNOWLEDGE of the distribution of blood to various vital organs and peripheral beds in the resting or basal state constitutes an important base line for proper insight to basic cardiovascular physiology. In addition, it is quite probable that many of the effects of extracorporeal circulation could be better understood if changes in regional distribution of blood flow were better known and further studied. The myriad of influences upon cardiovascular function imposed by extracorporeal circulation as now commonly used suggest that many changes can be effected in regional blood flow by perfusion itself. The following study is being presented in an effort to further elucidate some of the hemodynamic factors surrounding regional blood flow distribution in the dog under the influences of extracorporeal circulation. Methods Ten healthy mongrel dogs, each weighing from 11 to 16 kg (24.2 to 35.2 lb), were anesthetized with thiopental sodium, nitrous oxide, and succinylcholine, and