To ensure our survival, the brain continuously estimates important homeostatic and physiological variables, such as our hunger, thirst, and effort levels. This estimate relies on multiple signals, most prominently on interoceptive signals coming from inside the body (e.g., cardiac and respiratory signals). Here we tested the hypothesis that providing false feedback about these signals produces an interoceptive illusion, that is a misperception of one’s own physiological state. We show that giving participants false (faster) acoustic feedback about their heartbeats during an effortful cycling task induced the illusion of making more effort. Rather, participants did not report lower effort when slower acoustic feedback was provided, suggesting that the brain considers the potential costs of underestimating effort and fatigue levels.