Background: One of the sources of anxiety and fear among patients undergoing open-heart surgery is the possibility of experiencing pain, such as sternotomy-related chest pain. Giving them the chance to express their feelings about the potential pain may be effective in reducing their anxiety and may support their coping strategies. Objectives: To examine pain-related fear among patients undergoing open-heart surgery and to understand the underlying reasons of their fears. Methods: A qualitative interview based on Heidegger’s interpretative phenomenological approach was conducted adhering to the COREQ guidelines. Sixteen patients who were undergoing open-heart surgery in the following day were interviewed at the cardiovascular surgery ward of a university hospital. The organization and mapping of the qualitative data was done by using ATLAS.ti 8.0. Results: The patients who were afraid of experiencing pain after surgery seemed to be more concerned about open-heart surgery itself (such as pain from sternotomy and chest tubes) and the possibility of prolongation of postoperative pain. To cope with these fears, the patients employed a variety of social and self-coping strategies. Trusting the healthcare team, having a high pain tolerance, and having personal thoughts that take precedence over pain-related fear were the key factors explaining not being afraid of experiencing pain. Conclusions: This study provides a deeper understanding of the underlying reasons and the needs of patients in controlling their pain-related fears before open-heart surgery. Trusting the healthcare professionals is one of the main factors for patients to control their pain-related fears. To develop a supportive sense of trust and to help patients in controlling their pain-related fears, surgical nurses must dedicate enough time for understanding patients’ concerns while planning their nursing care plans. Future studies may focus on exploring the role of nursing interventions and multidisciplinary team approaches on the management of preoperative pain-related fear.