Introduction: Relative bradycardia, also known as Faget's sign, occurs when the heart rate does not increase in proportion to fever. Although it has been described for years in different infections, in daily practice it is rarely sought systematically and its clinical usefulness is not always taken into account. Objective: To determine whether relative bradycardia is useful in guiding diagnosis and prognosis in patients with febrile syndrome. Methods: A systematic review of the literature was conducted in PubMed, Scopus, Web of Science, and SciELO. Articles published between 1992 and 2024 that evaluated the relationship between body temperature and heart rate were included. Results: Twenty-four studies were included. Relative bradycardia was most frequently described in typhoid fever, dengue, legionellosis, and leptospirosis. Most studies showed high specificity, although sensitivity was variable. Its identification helped to better guide diagnosis, especially in resource-limited settings. Variability was also found between studies. Conclusions: Relative bradycardia is a clinical sign that can be useful in daily practice but is underutilized. Its value could be improved by standardizing diagnostic criteria and conducting more prospective studies.