Coronary artery bypass surgery (CABC) is a commonly performed surgical procedure for the treatment of blockages in the heart vessels. This surgical intervention aims to improve the blood circulation of the heart muscle of patients. However, after CABC, patients may experience symptoms arising from the effect of the operation. These symptoms include shortness of breath, chest pain, sleep problems and a general feeling of restlessness. These symptoms occur as a result of the operation and can limit the daily activities of patients, negatively affect their quality of life and make the rehabilitation process difficult.Diaphragmatic breathing exercise can be an effective strategy for managing symptoms after CABC. This exercise involves deep and controlled breathing and aims to strengthen respiratory muscles, increase lung capacity and improve respiratory efficiency.Diaphragmatic breathing exercise helps breathing occur more efficiently by reducing the movement of the chest wall and can reduce patients' breathing difficulties.After CABC, patients' sleep quality can often be negatively affected. Factors such as shortness of breath, pain, discomfort, and time spent in a hospital environment can cause decreases in sleep duration and quality. Sleep disorders can affect patients' rest and recovery processes, reduce their overall quality of life, and prolong the recovery process. Diaphragmatic breathing exercise may be a potential strategy to improve sleep quality. This exercise, which involves deep and controlled breathing as well as relaxation and stress reduction techniques, can improve sleep patterns by promoting relaxation.Diaphragmatic breathing exercise provides relaxation in the body by calming the sympathetic nervous system and can reduce stress during the sleep process. In this way, patients can experience a deeper and more restful sleep and feel more energetic when they wake up.Coronary artery bypass surgery (CABG) is a commonly used surgical method in the treatment of narrowing of the coronary arteries. This surgical procedure aims to improve blood circulation of the heart muscle and improves patients' quality of life. However, increased anxiety levels may be observed in patients undergoing CABG in the postoperative period. This anxiety can affect patients' rehabilitation process and negatively impact their quality of life.Therefore, effective interventions to reduce anxiety in CABG patients are being investigated. Anxiety is a common condition in patients undergoing CABG surgery and may increase in the post-surgical period. This anxiety can be caused by a variety of factors, including physical discomfort, the hospital environment, fear, uncertainty, and concerns about the future. Therefore, it is important to develop an effective intervention to reduce anxiety in CABG patients.Diaphragmatic breathing exercise is a technique used to control breathing and encourage deep breathing. This exercise is known to have positive effects such as reducing stress, providing relaxation and reducing anxiety. Therefore, it is thought that diaphragmatic breathing exercise may have a positive effect on anxiety in CABG patients. This exercise provides relief and relaxation by encouraging the correct use of respiratory muscles. Diaphragmatic breathing exercise involves rhythmically controlling breathing and expanding and contracting the abdominal area. This process helps reduce stress responses by activating the sympathetic nervous system and provide relief by activating the parasympathetic nervous system.The effect of diaphragmatic breathing exercise on anxiety is based on several mechanisms. Breathing deeply and slowly increases the amount of oxygen and reduces the amount of carbon dioxide in the body. This provides relief by reducing the release of cortisol and adrenaline, the body's stress hormones.At the same time, diaphragmatic breathing exercise improves mental state and reduces the effects of stress by providing focus and mental relaxation.This thesis study aims to investigate the effect of diaphragmatic breathing exercise applied to patients undergoing CABC on symptom severity, sleep quality and anxiety. Managing symptoms and improving patients' quality of life after CABC has become an important goal. Research in this field shows that diaphragmatic breathing exercise can reduce symptoms after CABC and reduce patients' general anxiety. However, the information in the literature shows that there are not enough and comprehensive studies on this subject. Therefore, this thesis study aims to evaluate the effect of diaphragmatic breathing exercise on symptom severity, sleep quality and anxiety in patients undergoing CABC. The study is conducted to evaluate the effect of diaphragmatic breathing exercise applied to patients undergoing CABC on symptom severity, sleep quality and anxiety. This study aims to investigate the effectiveness of the care provided by nurses to patients after CABC and its contribution to increasing patient outcomes.The importance of this study is that it has great potential for managing symptoms after CABC and improving patients' quality of life. Diaphragmatic breathing exercise is expected to be effective in reducing symptoms after CABC, allowing patients to improve their respiratory functions and general health status. Additionally, investigating the effects of this exercise on patients' sleep quality and anxiety may help nurses adopt a more holistic approach in healthcare delivery.The findings of this study may offer an effective intervention strategy that can be used in nursing practice in the care of patients after CABC. Diaphragmatic breathing exercise is expected to reduce post-CABC symptoms, improve patients' quality of life, and improve their general anxiety. Nurses can play an important role in implementing this intervention, guiding and supporting patients. Additionally, this study is concerned with identifying an intervention that has the potential to alleviate post-CABC symptoms. Reduction of symptoms, While patients' quality of life increases, their anxiety may decrease. This study has the potential to provide an effective intervention strategy that nurses can use to guide and support patients after CABC.