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Background: The determinants of left atrial (LA) reservoir function have not been clarified. Methods: To elucidate the effect of left ventricular (LV) contraction on LA reservoir volume (ΔVLA), volume change due to mitral annular downward motion and aortic root anterior motion, which are related to LV contraction during systole, was calculated in 72 consecutive subjects [42 patients without any cardiac disease (control group), 13 patients with heart failure with reduced ejection fraction (HFrEF group) and 17 with preserved ejection fraction (HFpEF group)]. LA volume was calculated using the modified Simpson's method of bi-plane 2-D echocardiograms. ΔVLA was the difference between the maximum and minimum LA volumes. LA volume change according to mitral annular motion (ΔVMA) and aortic root motion (ΔVAR) were calculated by assuming an oval frustum and dented wedge, respectively. Results: In the normal control group, ΔVAR + ΔVMA was 11.7 ml on average, correlating to ΔVLA (r = 0.55, p < 0.01), and the contribution rate to LA reservoir volume ((ΔVAR + ΔVMA)/ΔVLA) was 56% on average. In both, the HFrEF and HFpEF groups, ΔVAR, ΔVMA, and the contribution rate were significantly smaller than those in normal control group. Stroke volume correlated to ΔVAR and ΔVMA. The larger the maximum LA volume was, the smaller the contribution rate was. The smaller the rate was, the higher the systolic pulmonary artery pressure was. Conclusions: Both mitral annular motion and aortic root anterior motion, which are related to ventricular contraction, are important for the LA reservoir volume recruitment. [ABSTRACT FROM AUTHOR]