This review explores the neuropsychobiology of fear-induced bradycardia in humans, focusing on methodological advancements and recent research findings. Fear-induced bradycardia, a temporary decrease in heart rate in response to negative outcomes, has been used as a secondary measure to assess defensive responses in fear conditioning experiments. The review highlights the evolution of fear conditioning techniques and the importance of psychophysiological indices, such as skin conductance response (SCR) and fear potentiated startle (FPS), in studying fear learning and its physiological changes. It also discusses the cardiac neuroanatomy, including the role of the sympathetic and parasympathetic nervous systems in regulating heart rate. The history of fear-induced bradycardia is traced back to early studies in the early 20th century, with significant contributions from researchers like Notterman et al. who reported conditioned cardiac responses in fear conditioning paradigms. Recent studies have refined methods for measuring heart rate changes, such as beats per minute (BPM) and heart period (HP), and have explored the relationship between fear-induced bradycardia and individual differences, such as accelerators and decelerators. The review also examines controversial findings in fear-induced bradycardia research, emphasizing the importance of proper analysis methods and experimental designs. It highlights the use of heart rate variability (HRV) as an indicator of prefrontal inhibitory capacity and adaptability to environmental changes, suggesting that low HRV is linked to deficiencies in safety learning and extinction of fear responses. Finally, the review provides guidelines for using fear-induced bradycardia as a valuable psychophysiological measure in fear conditioning research, emphasizing the need for consistent and accurate data collection methods.This review explores the neuropsychobiology of fear-induced bradycardia in humans, focusing on methodological advancements and recent research findings. Fear-induced bradycardia, a temporary decrease in heart rate in response to negative outcomes, has been used as a secondary measure to assess defensive responses in fear conditioning experiments. The review highlights the evolution of fear conditioning techniques and the importance of psychophysiological indices, such as skin conductance response (SCR) and fear potentiated startle (FPS), in studying fear learning and its physiological changes. It also discusses the cardiac neuroanatomy, including the role of the sympathetic and parasympathetic nervous systems in regulating heart rate. The history of fear-induced bradycardia is traced back to early studies in the early 20th century, with significant contributions from researchers like Notterman et al. who reported conditioned cardiac responses in fear conditioning paradigms. Recent studies have refined methods for measuring heart rate changes, such as beats per minute (BPM) and heart period (HP), and have explored the relationship between fear-induced bradycardia and individual differences, such as accelerators and decelerators. The review also examines controversial findings in fear-induced bradycardia research, emphasizing the importance of proper analysis methods and experimental designs. It highlights the use of heart rate variability (HRV) as an indicator of prefrontal inhibitory capacity and adaptability to environmental changes, suggesting that low HRV is linked to deficiencies in safety learning and extinction of fear responses. Finally, the review provides guidelines for using fear-induced bradycardia as a valuable psychophysiological measure in fear conditioning research, emphasizing the need for consistent and accurate data collection methods.