The purpose of this experimental study was to evaluate the effect of preoperative teaching method on anxiety levels of the patients. This study consisted of 100 patients having open cardiac surgery. Of 100 patients 50 were placed in the intervention group while the remaining 50 were in the control group. The patients in the intervention group were given a planned teaching according to the patient education booklet. Patients in the control group were informed about pre- and postoperative routines by a nurse by the purpose of comparing anxiety levels of the patients in the intervention and control groups. The anxiety level of the patients in control and intervention groups was measured on the 3rd day after the operation by using the Self-Evaluation Questionnaire for State and Trait Anxiety Inventory. The mean postoperative state and trait anxiety score in the control group was slightly higher than the mean of the patients in the intervention group. There was no statistically significant difference in the state and trait anxiety scores between the groups, and the patients in the intervention group had lower scores than the patients in the control group. In addition, all patients in the intervention group stated that they were satisfied with the preoperative teaching given by the researcher.