The objective of this study was to understand the cognition of preoperative nursing instructions and to determine anxiety level in three stages of hospitalization of cardiac surgery patients. Evaluation of fear level of post cardiac surgery experience in intensive care unit by patient themselves and evaluation of relationships involving the cognition of preoperative nursing instruction between anxiety level and degree of fear in these patients. A-experimental study design was used. The convenience sample consisted of 31 patients from an immediate intensive care unit in a large hospital during a three-month period A nursing instruction survey questionnaire, the STAI Anxiety Scale, and a Fear Scale served as the data collection instruments. The study's results found were as follows:(1)the anxiety level of cardiac surgery patients decreased when Patients accepted preoperative nursing instructions, (2)perception of cognition and anxiety, there was no correlation between the degrees of, (3) the sources fear for patients open heart surgery patients in intensive care unit consisted of:dyspnea, suction, misunderstanding the disease process, the fact that nurses can't always stand bedside when the patient is in need of care and respiration incompatibility with the ventilator. The study provide the clinical nurses to understand the anxiety level and degree of fear concerning cardiac surgery patients. The manual of preoperative nursing instructions can be referenced by clinical nurses to teach cardiac surgery patients how to decrease pre-surgical anxiety levels and promote post operation recovery.