The objective of the present study was to compare pre- and postoperative pulmonary function tests in adult patients who had intubation periods greater and less than 24 hours following elective open heart surgery. Group 1 consisted of 91 patients (18 females and 73 males) gr, whose intubation periods were more than 24 hours (mean: 8.1+/-18.6 hours); and group 2 75 patients (13 females and 62 males) who had intubation periods less than 24 hours (mean: 13.25+/-3.60 hours). The pulmonary function test measurements were obtained from a vitalograph before and after the operation (just before being discharged from the hospital), All patients underwent cardiopulmonary physiotherapy and a rehabilitation programme during their hospital stay. The patients were similar in height and weight. The duration of hospitalization of the patients who had a prolonged intubation period was 17.26+/-9.7 days, while that of the control group was 10.64+/-2.04 days (P<0.0001). When the preoperative pulmonary function test values of each patient were compared with the expected values, the percent values of forced expiratory volume for one second, flow velocity of the mid-forced expiration and forced expiratory flow which were achieved by group 2 were significantly high compared to those of group 1 (P=0.014, P= 0.03 and P<0.0001, respectively). However, the percent values of forced vital capacity were similar. When the percent variations of the differences between the pre- and postoperative pulmonary function test values of the groups were compared, all values except the flow velocity of the mid-forced expiration, and forced vital capacity, were found to be significantly lower statistically in the group having a prolonged intubation period. As a result, it was determined that the patients whose preoperative pulmonary function test values were poor, had longer intubation periods and similarly, they continued to be worse after the operation. We believe that it is advantageous to apply more intensive pulmonary rehabilitation for prolonged periods to these patients in the postoperative period.