Cardiovascular reflexes may originate either within or outside of the heart. Most physicians are more familiar with those of extracardiac origin, such as the baroreflexes initiated from the arch of the aorta or the chemoreflexes which come from the carotid body. Of all the cardiovascular reflexes, among the least understood have been the cardiogenic chemoreflexes. This presentation considers two such reflexes which may have special importance in clinical medicine. The first of these is the Bezold-Jarisch reflex, which is depressor in nature and produces only moderate magnitude effects. The second is a hypertensive cardiogenic chemoreflex produced maximally by serotonin (5-hydroxytryptamine), is excitatory in nature and produces dramatically profound effects. In most respects these two cardiogenic chemoreflexes are physiological mirror images.