The aim of our study was twofold: 1) to establish a mathematical link between mean aortic pressure (MAP) and systolic (SAP) and diastolic (DAP) aortic pressures by testing the hypothesis that either the geometric mean or the harmonic mean of SAP and DAP were reliable MAP estimates; and 2) to critically evaluate three empirical formulas recently proposed to estimate MAP. High-fidelity pressures were recorded at rest at the aortic root level in controls (n=31) and in subjects with various forms of cardiovascular diseases (n=108). The time-averaged MAP and the pulse pressure (PP=SAP-DAP) were calculated. The MAP ranged from 66 to160 mmHg (mean(SD) =107.9(18.2) mmHg). The geometric mean, i.e., the square root of the product of SAP and DAP, furnished a reliable estimate of MAP (mean bias(SD) = 0.3(2.7) mmHg). The harmonic mean was inaccurate. The following MAP formulas were also tested: DAP+0.412 PP (Meaney et al. 2000); DAP+0.33PP+5 mmHg (Chemla et al. 2002); and DAP+[(0.33 + (heart rate x 0.0012)] PP (Razminia et al. 2004). They all provided accurate and precise estimates of MAP (mean bias(SD) = -0.2(2.9); -0.3(2.7) and 0.1(2.9) mmHg respectively). The implications of the geometric mean pressure strictly pertained to the central (not peripheral) level. It was demonstrated that the fractional systolic (SAP/MAP) and diastolic (DAP/MAP) pressures were reciprocal estimates of aortic pulsatility, and that the SAP times DAP product matched the total systemic resistance times cardiac power output product. In conclusion, although the previously described thumb-rules applied, the "geometric mean aortic pressure" appears more valuable as it established a simple mathematical link between the steady and pulsatile component of aortic pressure.