Consistent with a straightforward, time-domain interpretation of Westerhofs classic circuit diagram of the 3- element Windkessel, we have concluded that measured aortic pressure is the instantaneous sum of a constant (P∞), a Windkessel/reservoir pressure, and a wave-related pressure. According to our interpretation, the resistive element interposed between the left ventricle and the resistance-capacitance (RC) filter is, in fact, a hydraulic resistance in the proximal aorta that defines the wave-related pressure. The RC filter subserves the Windkessel/reservoir function and is distributed anatomically within the large arteries. The lower potential (pressure) of the RC filter (P∞) is not zero or even venous or mean circulatory pressure, but rather a higher pressure (∼30 – 40 mmHg) toward which aortic pressure declines asymptotically during diastole. As previously recognized, the Windkessel/reservoir pressure describes aortic diastolic pressure very precisely; in the new paradigm, the addition of the wave-related pressure provides the complement that describes systolic pressure equally precisely. This new interpretation has several potential implications for our understanding of hypertension. Diastolic hypertension would seem to be related most directly to alterations in reservoir pressure, particularly P∞ and reservoir resistance. Systolic hypertension may be a function of several factors: wave reflection, increased proximal aortic resistance, and decreased aortic compliance.