CLINICIANS and clinical physiologists would prefer to base an understanding of the function and regulation of the cardiovascular system on observations carried out in man. However, both ethical considerations and limitations in instrumentation mandate the study of laboratory animals, in which appropriate controls and interventions can be introduced. Whereas extremely important hemodynamic information has been obtained from studies of man, most of the knowledge of cardiovascular physiology and pharmacology is based on findings obtained in animal experiments, which have been conducted most frequently on animals in the anesthetized state, often with an open chest. The conclusions derived from these experiments . . .