Abstract： Objective:To investigate the effect of dexmedetomidine on heart rate variability (HRV) after aortic valve replacement (AVR).Methods:A retrospective case-control study was conducted, a total of 130 patients with AVR aortic valve disease were selected from the department of Cardiovascular Surgery in General Hospital of Northern Theater Command from January 2020 to April 2023, there were 74 males and 56 females, aged (58.07±9.38) years old, ranging from 28 to 74 years old.The patients were divided into A group, B group and C group according to the use of dexmedetomidine.A group was not treated with dexmedetomidine ( n=63), B group was given dexmedetomidine on demand ( n=38), and C group was routinely given dexmedetomidine according to the course of treatment ( n=29).The perioperative heart rate, incidence of atrial fibrillation and left ventricular ejection fraction were compared among the 3 groups.The HRV indexes of the 3 groups were compared before and after operation, including the percentage of successive RR intervals that difer by more than 50 ms, root mean square of successive differences, standard deviation of NN intervals (SDNN), mean of the standard deviations of all NN intervals for all 5-minute segments of the entire recording (SDNNIDX), standard deviation of the averages of NN intervals in all 5-minute segments of the entire recording (SDANN), percentage of successive RR intervals that difer by more than 20 ms. Results:On the 7 days after operation, SDNN[A group 53.40 (49.40, 66.10)ms, B group 62.70 (54.68, 73.68) ms, C group 62.50 (50.80, 78.15)ms], SDANN [A group(51.80±11.42)ms, B group(60.96±14.8)ms, C group(60.06±16.01)ms], SDNNIDX[A group(17.55±5.35)ms, B group(21.49±7.56)ms, C group(19.08±5.62)ms], the differences were statistically significant ( P<0.05).Compared with group C, when patients in group B had severe stress symptoms, the decrease of SDNN, SDNNIDX and SDANN was greater, and the impact on HRV was greater, while for patients in group C, the decreasing trend of SDNNIDX, SDNN and SDANN were moderate even with the increase of drug dosage. Conclusions:Dexmedetomidine has an effect on SDNN, SDNNIDX and SDANN of patients after AVR.Although the dose of patients given according to the course of treatment increases, the decline trend of above-mentioned indexes is more moderate after operation.