Purpose: The purpose of this study was to identify the intensity and types of discomfort caused by an endotracheal tube in patients during ventilator therapy after cardiac surgery, and to analyze the differences in the intensity and types of discomfort by sociodemographic and clinical characteristics and characteristics related to endotracheal tubes. Methods: The intensity of discomfort was measured using an 11-point numeric rating scale and the types of discomfort were measured using a 4-point numeric rating scale. Sociodemographic and clinical characteristics and characteristics related to endotracheal tube were collected by observation and the electronic medical chart using a structured questionnaire. Results: The mean intensity of discomfort in patients due to endotracheal tubes was 6,91 points, 84% of patients reported discomfort over 5 points, The most severe discomfort was pain during endotracheal suctioning, and dry mouth and breathing difficulties were also found to induce discomfort. Patients who had more severe surgical site pain, longer duration of intubation and higher cuff pressure demonstrated more severe discomfort due to the endotracheal tube. Conclusion: These results can be used as basic data for developing nursing intervention to relieve the discomfort caused by endotracheal tubes in patients during ventilator therapy.