An increasing number of procedures over the past two decades for aortic stenosis (AS) reflects the combination of an aging population and less invasive transcatheter options. As a result, the hemodynamics of the aortic valve (AV) have gained renewed interest to understand its behavior and to optimize patient selection. We studied the hemodynamic relationship between pressure loss (ΔP) and transvalvular flow (Q) of the normal AV as well as the impact of a variable supravalvular stenosis. Our mechanistic study included 11 healthy swine monitored during dobutamine stress and followed by acute aortic banding to simulate AS. Hemodynamics were continuously recorded, and transvalvular ΔP versus Q were analyzed using proportional and linear models. During dobutamine infusion, normal valves exhibited a highly linear relationship between ΔP and Q (median R2 of 0.93). Progressive aortic banding eventually displayed a highly linear relationship between an increasing ΔP and the decreasing Q, characterized by a constant systemic circulatory resistance (median R2 of 0.91). Consequently, a normal AV can be described by a single parameter: its resistance, median 0.37 Wood units (WU) in swine. During dobutamine stress and aortic banding, the systemic bed behaves like a constant and stable resistance, median of 11.9 WU in swine. These findings carry significant implications for quantifying normal and diseased AV behavior and potentially might improve patient selection and treatment outcomes.NEW & NOTEWORTHY This study demonstrates that the normal aortic valve functions like a resistor with a proportional pressure loss ΔP versus transvalvular flow Q relationship. During dobutamine stress and progressive aortic banding, a "load line" of constant resistance characterizes the systemic circulation. Consequently, during stress conditions, the relative pressure loss over a stenotic aortic valve (the stress aortic valve index, SAVI) quantifies the relative reduction in maximal flow. Potentially, SAVI might optimize patient selection for procedures to treat aortic stenosis.