Self-efficacy, understood as confidence in one’s ability to execute specific tasks successfully, is a key factor in the performance of healthcare professionals in emergency situations. In the context of Advanced Cardiovascular Life Support (ACLS), which requires quick decision-making and the precise execution of technical skills, self-assessment of one’s abilities is essential to ensure quality care and patient safety. However, the question arises: could overconfidence compromise actual performance in critical settings? Aim: To evaluate ACLS self-efficacy among healthcare professionals in public hospitals and compare it with their actual performance. Methods: 90 healthcare professionals from five public hospitals in a central region of Chile were included. ACLS self-efficacy was measured using an instrument specifically designed for emergency care, while practical ACLS skills were evaluated based on the American Heart Association® guidelines. Additionally, cognitive skills were assessed using a tool developed for this study. Self-efficacy was then compared to actual performance in both practical and cognitive skills. Results: This study identified a significant discrepancy between self-reported confidence and actual ACLS skills. Although many professionals reported high confidence levels in their abilities, their practical and cognitive performance was considerably lower than expected. Conclusions: This study reveals a significant gap between self-efficacy and actual performance in ACLS, suggesting that professionals with lower skill proficiency overestimate their abilities due to metacognitive biases, aligning with the Dunning-Kruger effect - potentially impacting the quality of patient care. Addressing this discrepancy through targeted education and practical simulations is crucial to improving emergency outcomes and patient safety.