Cardiac interoception exhibits tight coupling with brain activity, deeply engaging in emotional behavior. However, the neural mechanisms underlying how heart activity influences brain emotional processing remain poorly understood. This study introduced the heartbeat oscillatory potential (HOP), a novel EEG-based index time-locked to ∼0.1 Hz heartbeat oscillations, and examined the change of HOP during 0.1 Hz slow-paced breathing (SPB). Resting-state data from 108 healthy adults revealed that HOP was involved in the frontal and parietal cortices. Data collected from 37 subjects showed that SPB increased HOP in a spatial- and phase-dependent manner, with increased HOP in the right prefrontal cortex around the peak of the ∼0.1 Hz heartbeat oscillations, mediated the association between the heartbeat oscillations and enhanced emotional control. These findings underscore the pivotal role of the right prefrontal cortex in linking cardiac interoception, providing insights into the benefits of SPB on emotional control from a heart-brain interaction perspective.