Interoception it has a large influence on how animals make decisions and is necessary to adjust internal body function to the organism’s needs, such as during rest or hunting. The heart is essential in the process to adapt the animal to changing circumstances by increasing or decreasing its rate. Heart rate modulation occurs through the communication between sensory and motor ganglia of the autonomic nervous system. The vagal neurons transmit information to the heart and send information via the autonomic nervous system to the central nervous system. How they interact to change heart activity, however, is not well understood. Here, we study interoception of the heart in a vertebrate system, the zebrafish larvae, by investigating the vagal sensory neurons and their role for the organism.To address the neuronal circuits regulating the heart, we want to understand what cell types are present within the vagal sensory neuron population using single cell transcriptomics. We validate these putative cell types through in situ hybridization by localizing them within the vagal ganglia. Through sparse labelling methods, we reconstruct morphologies of previously identified neurons and trace the circuit from the heart to the brain. This allows us to investigate which populations of neurons innervate the zebrafish heart and how they connect the heart to the autonomic and central nervous systems. Altogether, the project will give us a better understanding of brain-body communication and open new questions on how visceral sensation can change brain function and internal state of the animal.