Heart rate variability (HRV) was measured in 29 normal subjects (group I )

2F patients with cardiac function of NYHA Class Ⅰ to Ⅱ (group Ⅱ) and 27 patients with Cardiac function of NYHA class Ⅲ to Ⅳ(group Ⅲ)

The time domain indices of HRV wore obtained from 24 - hour ambulatory . recordings

including SDNN

SDANN

SDNNIDX

rMSSD

pNN50 and HRVI. Frequency domain indices were obtained from 10 minutes electrocardiographic recordings

including LF

HF and the ratio of LF/HF. The average values of LF

HF and all time domain indices were orderly reduced from groupⅠ to groupⅡ

the differences between any two gruops were atatistically significant . The ratio of LF / HF orderly increaaed from group Ⅰ to group Ⅲ. These findings indicated that HRV was reduced in patients with chronic heart failure and therefore the cardiac parasympathetic activity was also reduced. The degree of parasympathetic dysfunction was related to the severity of heart failure.