Background: There are 2 different methods of suctioning the airway: the open tracheal suction system (OTSS) and the closed tracheal suction system (CTSS). The aim of this study was to compare the efficacy of the OTSS and the CTSS in maintaining the stability of hemodynamic and oxygen parameters in patients after cardiac surgery. Methods: This randomized controlled clinical trial was conducted on 60 patients who were under mechanical ventilation after cardiac surgery. The study population was randomly divided into the OTSS and CTSS groups. All the patients were at least 18 years old and hemodynamically stable. Hemodynamic parameters such as systolic and diastolic blood pressures were measured. Oxygen parameters such as the saturation percentage of arterial blood oxygen (SpO2) and the oxygen pressure of arterial blood (PaO2) were measured before, immediately, and also 3 and 5 minutes after suction. All the parameters were compared between the 2 groups. Results: The mean heart rate, the mean systolic blood pressure, and the mean arterial blood pressure showed a higher increase in the OTSS group (P<0.05), as the mean PaO2 and SpO2 were higher in the CTSS group (P<0.05). Conclusions: The CTSS caused fewer disturbances in the hemodynamic and oxygen parameters in comparison with the OTSS in our study population. Therefore, disturbances in the aforementioned parameters can be avoided by using the CTSS in patients undergoing cardiac surgery. (Iranian heart Journal 2018; 19(3): 51- 59)