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<jats:p> <jats:italic>Background</jats:italic> A noninvasive measure of left ventricular (LV) chamber stiffness (K <jats:sub>LV</jats:sub> ) would be clinically useful. Our theoretical analysis predicts that K <jats:sub>LV</jats:sub> can be calculated from the time for deceleration of LV early filling (t <jats:sub>dec</jats:sub> ) by </jats:p> <jats:p> <jats:disp-formula> <jats:tex-math notation="LaTeX">\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \[K_{LV}{=}\frac{{\rho}\ {\cdot}\ L}{A}\ {\cdot}\ (\frac{{\pi}}{2}\ {\cdot}\ \frac{1}{t_{dec}})^{2}\] \end{document}</jats:tex-math> </jats:disp-formula> </jats:p> <jats:p>where ρ=density of blood, L=effective mitral length, and A=mitral area.</jats:p> <jats:p> <jats:italic>Methods and Results</jats:italic> We tested this hypothesis in eight conscious dogs instrumented for measurement of LV pressure (P) with use of a micromanometer and volume (V) with use of sonomicrometers. K <jats:sub>LV</jats:sub> was determined as the slope of the late diastolic portion of the LV P-V loop. K <jats:sub>LV</jats:sub> was varied from 0.99±0.35 to 2.58±0.92 mm Hg/mL with use of three graded doses of phenylephrine. We assumed that ρ=1.0 and that L/A=3.4. Thus, we predicted that K <jats:sub>LV</jats:sub> =(0.08/t <jats:sub>dec</jats:sub> ) <jats:xref ref-type="bibr"> <jats:sup>2</jats:sup> </jats:xref> . The LV filling pattern was determined from the derivative of LV volume (dV/dt). t <jats:sub>dec</jats:sub> was measured from peak early filling to the end of early filling. Predicted K <jats:sub>LV</jats:sub> and actual K <jats:sub>LV</jats:sub> were closely correlated ( <jats:italic>r</jats:italic> =.94, SEE=0.06 mm Hg/mL, <jats:italic>P</jats:italic> &lt;.05). The regression line was close to the line of identity (slope=0.95, intercept=0.13 mm Hg/mL). Dobutamine did not alter the relation between t <jats:sub>dec</jats:sub> and K <jats:sub>LV</jats:sub> . t <jats:sub>dec</jats:sub> determined from the mitral valve flow velocity measured with Doppler echocardiography correlated well with that measured by dV/dt ( <jats:italic>r</jats:italic> =.89, <jats:italic>P</jats:italic> &lt;.01) but was 0.02 seconds longer. K <jats:sub>LV</jats:sub> -calculated t <jats:sub>dec</jats:sub> from the corrected Doppler t <jats:sub>dec</jats:sub> provided a good estimate of measured K <jats:sub>LV</jats:sub> ( <jats:italic>r</jats:italic> =.75, SEE=0.5 mm Hg/mL, <jats:italic>P</jats:italic> &lt;.01). </jats:p> <jats:p> <jats:italic>Conclusions</jats:italic> LV chamber stiffness can be determined from the time for deceleration of LV early filling, which can be measured noninvasively. </jats:p>