Despite advances in post-resuscitation care of patients with cardiac arrest (CA), the majority of survivors who are treated after restoration of spontaneous circulation (ROSC) will have sequelae of hypoxic-ischemic brain injury ranging from mild cognitive impairment to a vegetative state. Current recommendations suggest using a multimodal approach to predict poor prognosis, meaning combining markers together. Yet, a substantial proportion of patients do not have a clear prognostic evaluation even when applying the latest ESICM recommendations algorithm published in 2021. It is therefore important to identify new prognostic markers to predict both unfavorable and favorable outcomes. Data regarding the pathophysiological mechanisms of post-anoxic encephalopathy suggest a diffuse anoxo-ischemic injury. However, post-mortem neuropathology data suggest that these lesions do not uniformly affect neuroanatomical structures, with some regions (especially hippocampal and insular) appearing more sensitive to anoxia. Conversely, the brainstem appears less affected by anoxic lesions. Under physiological conditions, there are interactions between the heart and the brain, and between the brain and the heart mainly related to the autonomic nervous system, through interactions between central cortical control structures (especially insular) and brainstem structures (at the level of the bulb) and peripheral structures of the heart. Exploring the pathophysiological mechanisms of heart-brain interactions post-CA could thus help better understand the pathophysiology of anoxo-ischemic encephalopathy, before considering potential therapeutic targets. Furthermore, this heart-brain dysfunction could have prognostic value. Indeed, recent studies in healthy subjects and patients with consciousness disorders suggest that autonomic nervous system activity measured by brain-heart interactions could be a reliable marker of consciousness and cognitive processing. These coupled heart-brain interactions can be evaluated through synchronous electroencephalogram (EEG) and electrocardiogram (ECG) recordings, as there are coupled interactions between the signals of these two organs. The existence of abnormal brain-heart coupling could be associated, on the one hand, with the severity of post-anoxic encephalopathy, and on the other hand, with neurological prognosis in patients with persistent coma post-CA. This ancillary study of a multicentre prospective cohort HEAVENwARd study (NCT06044922) will assess the prevalence and prognostic value of bilateral brain-heart interactions in comatose patients after CA.