Brain dynamics are usually considered to be constrained by brain-related parameters, such as anatomical connectivity and conduction delays, or by external factors, such as the stimulus to be processed. This classical point of view ignores the fact that the brain constantly monitors bodily inputs, in particular from life-supporting organs such as the heart or the stomach. I will present recent evidence that visceral inputs constrain brain dynamics, as measured in humans with resting-state magneto-encephalography, functional MRI, or single-unit recordings. From a functional point of view, the neural monitoring of visceral inputs may play a fundamental role by generating an egocentric reference frame, from which first-person perspective, or subjectivity, can develop. I will present data showing that neural responses to heartbeats in the default-network play a functional role as they encode self-relevance in spontaneous thoughts but also predict subjective visual experience. Visceral-brain interactions might thus represent a core mechanism constraining both brain dynamics and « cold » cognitive processes.