Understanding the patient's safety implies the efforts and activities that are taken to ensure that all procedures and the environment in providing healthcare provide the desired outcome of the patient's treatment. The World Health Organization defines patient safety as "preventing, eliminating and improving the protection against unwanted events during healthcare". Patient's safety is one of the biggest challenges and imperatives in the healthcare system because health care quality is best reflected at the patient's safety level. Patient's safety can be evaluated in several ways: the physical safety of the patient in the operating room, the positive psychological environment for the patient, the safety of medical procedures, and computer security / security from unauthorized access and / or data theft. The nurses of the instrumentalists in their daily work primarily care about the patient's safety in the operating room environment to ensure that the surgical procedure is safe and without complications for the patient. The team environment in the cardio surgery which is consisted of health care professionals of different levels of education should strive to believe that thinking, planning, decisions and actions are better when working with common forces, since the operating room is a place where everything does not depend on one individual. Enhanced technology and availability of equipment as an important component in the development of quality healthcare for patients are positive, but of course there's a room for potential errors in the operating room. Making a patient safe is a professional responsibility of a nurse and involves professional knowledge. Each nurse should respect the principles of patient's rights, ethical and professional principles that are in the function of patient protection. In all patients, there is an increased risk of complications and death as they are subjected to surgical interventions. Even routine surgery requires complex coordination of surgeons, anesthetics, nurses and auxiliary staff to provide timely and effective care. Work experience, work organization, good communication in the teams are key factors of the care of patient's safety. The surgical checklist is one of the ways to improve patient safety in theoperating room. The application of the safety checklist for surgical procedures significantly improves patient safety, and thus the outcome of the operation itself.