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Background and aim: Chronic pressure overload due to severe aortic stenosis (AS) leads to compensatory hypertrophy along with fibrosis within myocardial extracellular matrix (ECM). Radial component of LV systolic function in the long course of disease is preserved or even improved contrary to LV longitudinal systolic function, that deteriorates early. We hypothesized that elastin and collagen cross – linking density influence left ventricular function in severe AS.Methods: Echocardiographic examination was performed in 40 consecutive patients (mean age 65±11 years, 19 men) with calcific severe AS without prior myocardial infarction qualified for aortic valve replacement (AVR). All patients were in sinus rhythm. LV longitudinal systolic function was expressed as mean mitral annular displacement (mean MAD) calculated from four mitral annulus aspects and mean mitral annular displacement index (mean MAD index) (mean MAD/longitudinal LV diameter).The endomyocardial biopsies obtained during AVR were used to evaluate total myocardial collagen content expressed as hydroxyproline/alanine ratio (H/A), collagen cross-linking density expressed as pirydynoline/hydroxyproline ratio (P/H) and elastin cross-linking density expressed as desmosine/hydroxyproline ratio (D/H). All biopsies analysis was performed by a method of liquid chromatography-mass spectrometry (LCMS).Results: Mean AVA = 0.58±0.24 cm2, mean AVmax = 5,03±0,81 m/s, mean AV meanPG = 63±20 mmHg, mean EF = 70±13 %, mean MAD = 1.8±0.2 cm, mean MAD index = 12.7±2.6 %. Mean H/A = 4.4±2.5 μmol/mmol, mean P/H = 2.9±1.0 μmol/mmol, mean D/H = 7,4±3,7 μmol/mmol. There was no correlation between LVEF and H/A (r = -0.15, p = NS), LVEF and P/H (r = -0.29, p = NS), LVEF and D/H (r = 0.29, p = NS). There was significant negative correlation between mean MAD and P/H (r= -0.3161, p < 0.05), and positive correlation between mean MAD index and D/H (r=0.3324, p < 0.05). There was no correlation between total collagen content expressed as H/A and mean MAD (r = -0.059, p = NS) and mean MAD index (r = -0.007, p = NS). Conclusions: LV longitudinal function in severe AS with preserved EF is influenced by mature (cross-linked) collagen and elastin content, rather than total collagen content within ECM.