Effects of each of these three receptors sets (carotid sinus, aortic arch, and cardiopulmonary)on heart rate are well documented. Quantitative aspects of their composite effects are still incompletely understood. Focus will be upon characterizing this quantitative relationship by modeling this multiple pressure receptor-heart rate reflex system. The baroreceptors will be pertubed by mechanical and pharmacological means and the reflex heart rate responses will be evaluated.