Somatic symptoms without a sufficient medical explanation are a key characteristic of somatoform disorders. Models addressing somatoform disorders posit that both biological (e.g., autonomic arousal, body signals) and psychological factors (e.g., attentional bias, anxiety) contribute to somatic symptom generation. This chapter focuses on ascending and descending communication between the brain and the body, with a particular emphasis on cardiac signals. Cardiac parameters indicating descending brain–body communication include heart rate (variability), blood pressure (variability), baroreflex sensitivity, and pre-ejection period. They can be used to quantify autonomic arousal. Among cardiac parameters indicating ascending brain–body communication are cardiac interoceptive accuracy and heartbeat-evoked potentials, which reflect the perception of body signals, cortical representation of cardiac signals and attention focused on cardiac sensations. Somatoform disorders may be associated with higher heart rate and lower heart rate variability associated with parasympathetic activity, higher attentional resources focused on cardiac signals, but impaired cardiac perception. Cardiac signals are suitable to confirm some key assumptions of theoretical models, such as autonomic hyper-arousal or an attentional bias toward body signals. Novel treatment approaches based on ascending/descending cardiac signals may be used to reduce somatoform symptom severity.