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Objective Anovel index based on frequency-domain analysis of heart rate variability (HRV) was tested on patients with reduced left ventricular systolic function.This index,namely VHFI,was defined as the very high frequency (VHF) component of the power spectrum normalized to represent its relative value in proportion to the total power minus the very low frequency component.Methods Patients (n=130) were divided into a study group,consisting 66 patients with decreased left ventricular systolic function,and a control group,consisting 64 patients with normal heart structure and function and without severe coronary artery stenosis (＜50%).Results VHFI in the study group was significantly higher than that in the control group (19.17±13.35 vs 11.37±10.77,P＜0.001).Cardiac events occurred in 18 patients during follow-up (33.34±3.26 months).Defining the positive test as VHFI =15 and negative test as VHFI ＜15,achieved a sensitivity of 57.58% and a specificity of 78.13% for predicting decreased left ventricular systolic function,and achieved a sensitivity of 66.67% and a specificity of 64.29% for predicting cardiac events.Univariate Cox regression analysis showed that positive VHFI test was an independent variable in predictive cardiac events.Conclusions The results suggest that VHFI is a useful tool for quick evaluation of left ventricular systolic function and prediction of prognosis.