The cortical processing of cardiac afferent input can be studied by means of event-related potentials (ERP), in which characteristic brain waves are seen to accompany rhythmic activity of the heart. In the present paper, results from three studies, investigating the heartbeat-evoked potential are summarized. These studies demonstrated that (a) cardio-afferent input is projected primarily to fronto-cortical areas; (b) typically, this activity is reflected as a broad positive wave form in a range of 300-600 ms after the EKG R-wave; (c) psychological factors such as level of attention and motivation exert influences on the heartbeat-evoked potential which are comparable to effects known from exteroceptive evoked potentials. On the basis of these data we infer that cardio-afferent input is for the most part transmitted along visceral fibers and that the cortical processing of cardiac activity is similar to the processing of external stimuli.