The period 1964-1976 consolidated the autonomic nervous system as the central controller of cardiovascular reactivity, integrating pharmacologic separation of sympathetic and parasympathetic inputs with direct monitoring of blood pressure and heart rate under varying states of activity and sleep. Methodological advances enabled by this era—such as controlled drug challenges, nocturnal arterial pressure measurements, and the nascent use of heart rate variability analyses—facilitated quantification of autonomic balance during exercise, rest, and aging. These studies jointly framed reactivity as a reflection of dynamic autonomic regulation rather than isolated cardiac responses, thus guiding subsequent research into baseline autonomic tone and cardiovascular risk. Historical Perspective: The work of this period laid a coherent, testable paradigm that connected parasympathetic predominance at moderate workloads with sympathetic dominance at higher demands, and tied baroreflex sensitivity and sleep-stage regulation to long-term cardiovascular outcomes. In doing so, it anchored the concept that central autonomic control underlies reactivity across physiological states, a viewpoint that shaped both clinical assessment and mechanistic inquiry for decades to come.