Background: Cardiac surgery is the largest consumer of blood products in medicine; although believed lifesaving, transfusion carries substantial adverse risks. Aim of the study: evaluate the effect of blood transfusion precautions on patient's outcomes undergoing open heart surgery. Patients and Methods: A quasi experimental design was adopted. A total of 60 adult patients post open heart operations divided equally into two groups (study group & control group). Tools: tool one; Patient Assessment Sheet; Part (I) Socio-demographic data, Part (II) Clinical Data, Part (III) Blood Transfusion observation Sheet. Tool two; Administering a Blood Transfusion Checklist. Results: The study group stayed less duration in the hospital and ICU than the control group with statistical significance difference as regard hospital stay in which p < .02 and statistical significance difference as regard ICU stay in which p < .000. As regards abnormal reaction during blood transfusion half of the control group had fever compared with one third of the study group. Recommendation & Conclusion: it can be concluded that, the applying of blood transfusion precautions on patients undergoing open heart surgery was successful in reducing hospital and ICU length of stay and complications of blood transfusion, and recommended that, hospital should provide ongoing quality programs for health care professionals.