The aim of this study was to examine the role of cardiac interoception on self-regulated (Experiment 1) and externally prescribed (Experiment 2) exercises. Cardiac interoception was assessed using heartbeat tracking and discrimination tasks in both experiments. Based on heartbeat discrimination performance, participants were partitioned into groups demonstrating GOOD and POOR cardiac interoceptive accuracy. In Experiment 1, 20 participants completed two self-regulated 20-min cycling tasks at two intensities (light rated physical exertion [RPE on Borg Scale = 10] vs. hard-to-very hard, RPE = 16). During self-regulated exercise, the POOR cardiac interoception group showed lower differences in their exercise work rates and physiological responses between light and hard-to-very hard intensity exercises. These differences were partly attributable to a higher work rate over the first 5 min of light intensity exercise and a higher initial rate of work in the first min of hard-to-very hard intensity exercise. In Experiment 2, 15 participants completed an externally prescribed, constant-load cycling task performed at 80% of the peak power output, to task failure. During externally prescribed exercise, GOOD and POOR groups did not differ in their time-to-task failure nor in their physiological and perceptual responses to the exercise. Together these findings demonstrate that individual differences in interoceptive accuracy influence the regulation of self-paced exercise but do not affect externally prescribed exercise tolerance under constant load.