en Cardiovascular Physiology/Pharmacology Cardiovascular Physiology/Pharmacology Review Review <div style="text-align: justify;"><span class="fontstyle0"><strong>Introduction:</strong> </span><span class="fontstyle2">Heart rate variability represents the performance of the cardiac autonomic nervous system (ANS) and is defined as the fluctuation of beat-to-beat between two successive R-waves (RR intervals). Accordingly, addressing the actions of the ANS in sickle cell disease helps in identifying the possible risk factors of sudden death. The clinical staging of the disease improves the diagnosis and the quality of the treatments. </span><strong><span class="fontstyle0">Methods: </span></strong><span class="fontstyle2">This systematic review analyzed the data of the basal autonomic reactions in sickle cell anemia (SCA) and sickle cell trait (SCT) patients compared to healthy people. In this study, 441 articles were retrieved from PubMed, ProQuest, SCOPUS, Embase, and Web of Science databases. Some of them were removed based on the inclusion and exclusion criteria, and finally, seven articles remained for analysis. </span><span class="fontstyle0"><strong>Results:</strong> </span><span class="fontstyle2">The data analysis of the included studies demonstrated that the vagal modulation at the basal condition decreased in SCA or SCT patients compared to the control group. </span><span class="fontstyle0"><strong>Conclusion:</strong> </span><span class="fontstyle2">The sympathovagal balance was altered in SCA or SCT patients, and an increasing trend was observed in sympathetic nerve activities.</span></div> Heart rate variability, Sickle cell anemia, Sickle cell trait, Autonomic nervous system 104 118 http://ppj.phypha.ir/browse.php?a_code=A-11-1140-2&slc_lang=en&sid=1 Esmaeil Akbari 3200319475328460030901 3200319475328460030901 No Department of Physiology, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran Reza Alizadeh-Navaei 3200319475328460030902 3200319475328460030902 No Gastrointestinal Cancer Research Center, Mazandaran University of Medical Sciences, Sari, Iran Motahareh Rouhi Ardeshiri m.roohi@mazums.ac.ir 3200319475328460030903 3200319475328460030903 Yes Department of Physiology, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran