Aim: We aim to determine the preoperative anxiety levels of patients with open-heart surgery and examine the relationship between anxiety levels and postoperative complications. Material and Methods: In our prospective study, 200 patients who will undergo open-heart surgery preoperative anxiety levels were measured using the Hamilton anxiety scale (HAM-A). Anxiety levels and the development of complications were investigated. Results: Preoperative anxiety was more common in females (p=0.001). The length of stay in the intensive care unit (p=0.006) and the hospital stay (p=0.005) were found to be longer in patients with high anxiety. It was observed that high preoperative anxiety severity increased the risk of developing postoperative complications (p=0.000024). Conclusion: We can say that preoperative anxiety, which is not considered very important, is seen more frequently than expected for patients who will undergo open-heart surgery. In our study, it was observed that high anxiety levels increased the risk of postoperative complications.