BACKGROUND This study aimed to investigate the relationship between the inferior vena cava respirophasic variation (IVC collapsibility index [IVCCI]) and the general heart end-diastolic volume index (GEDVI). By determining the above relationship, we could evaluate the utility of IVCCI as an indicator. MATERIAL AND METHODS Forty-two septic patients were finally enrolled in this study. The inferior vena cava's diameter was measured with the largest at the end of expiration (IVC3) and with the smallest at the end of inspiration (IVCi) on the ultrasound (IVCCI=[(IVCD e - IVCD i)/IVCD e] ×100%). The central venous pressure (CVP), cardiac index (CI), and GEDVI were also measured at least 3 times. After fluid resuscitation therapy, the patients with a CI increase induced by more than 15% and less than 15% were classified as the positive response group (PRG) and the negative response group (NRG), respectively. RESULTS After treatment, the average levels of CVP, CI, and GEDVI were significantly higher (P<0.01) in both groups, whereas the IVCCI was reduced. CVP, CI, and GEDVI were negatively correlated with IVCCI in both groups. The correlation coefficient between IVCCI and GEDVI was the greatest (correlation coefficient in the PRG group was 0.889 and in the NRG group it was 0.672). The ROC curve analysis indicated that IVCCI illustrated the best area under the curve, with a sensitivity of 100% and specificity of 100%, and a cut-off value of 12.9% to predict GEDVI <600 ml/m2 in the PRG group. CONCLUSIONS IVCCI was a good predictor of low-volume state. The IVCCI appears to be a valuable and non-invasive index for the estimation of elevated GEDVI during fluid resuscitation in septic shock patients.