Interoception involves the processing of sensory information relevant to physiological functioning and is integral to building self-awareness, emotional states, and modulating social behaviors. With the role of interoception in emotional processing and social functioning, there is growing interest in characterizing interoception in autism spectrum disorder (ASD), yet, there are mixed results regarding cardiac interoceptive accuracy in ASD. In this study, we explored the neural basis of cardiac interoception using an fMRI heartbeat-counting task in order to assess neural correlates of primary interoception. We predicted that interoceptive-specific response in the insula, a "hub" for interoception, would be related to ASD symptomatology. We investigated the relationship of insula responses during cardiac interoceptive focus and a self/caregiver-reported autism-related symptom scale (Social Responsiveness Scale-2 (SRS)). Participants included 46 individuals with autism spectrum disorder (ASD) (age 8-54, mean = 19.43 ± 10.68 years) and 54 individuals with typical development for comparison (TC, age 8-53, mean = 21.43 ± 10.41 years). We found no significant difference in cardiac interoceptive accuracy or neural response to cardiac interoception focus in ASD. Several insula subdivisions had a curvilinear relationship to age, peaking in early adulthood. Interoceptive-specific insula response was associated with adult self-report SRS scores; this association differed by diagnostic group and was not present for caregiver-reported scores. This work suggests that (a) there is no global deficit in cardiac interoception in ASD, but integrating interoceptive cues with social information may distinguish individuals with ASD, and (b) there is a developmental trajectory for interoceptive processing in the insula that may be relevant for socio-emotional health. Autism Res 2020, 13: 908-920. © 2020 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: We use internal sensory information from the body, such as signals from the heart, to understand our emotional response to the external world. We measured how accurately people with autism feel their heartbeat and how the brain responds to this type of information. We found no differences between the autism and comparison groups in how the brain senses heartbeats, or in how accurately people feel their heartbeats. However, for people with autism, brain responses while sensing heartbeats were related to social difficulties. This work suggests people with autism may use internal and external information in a different way.