Performance monitoring is a vital aspect of successful learning and decision-making. Performance errors are reflected in the autonomic nervous system, indicating the need for behavioural adjustment. As part of this response, errors cause a pronounced deceleration in heart rate, compared to correct decisions, and precede explicit awareness of the stimulus-outcome contingencies. However, it is unknown whether those signals are present and able to inform instrumental learning without conscious awareness of the stimuli, where explicit performance monitoring is disabled. With mixed evidence for unconscious instrumental learning, determining the presence or absence of autonomic performance monitoring can shed light on its feasibility.Here, we employed an unconscious instrumental conditioning task, where successful learning is evidenced by increased approach responses to visually masked rewarding stimuli, and avoidance of punishing stimuli. An electrocardiogram (ECG) assessed continuous cardiac activity throughout the learning process. Natural fluctuations of awareness under masking permitted us to contrast learning and cardiac deceleration for trials with, versus without, conscious stimulus awareness. Our results demonstrate that on trials where participants did not consciously perceive the stimulus, there was no differentiation in cardiac response between rewarding and punishing feedback, indicating absence of performance monitoring. In contrast, consciously perceived stimuli elicited the expected deceleration upon error commission. This result suggests that, in unconscious instrumental learning, the brain cannot acquire implicit knowledge of stimulus values, rendering correct instrumental choices impossible. This evidence provides support for the notion that consciousness might be required for flexible adaptive behaviour, and that this may be mediated through bodily signals.