Background: acute coronary syndrome refers to a group of potentially fatal disorders caused by acute myocardial ischemia, such as unstable angina, non-ST-segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI). Reducing morbidity and mortality requires early detection, quick risk assessment, prompt reperfusion, and medical treatment guided by recommendations. About one-third of all fatalities in people over 35 are caused by this illness, which continues to be the world's top cause of death. Objective: To evaluate the effect of nursing instructions on Selected outcome among patients with Acute Coronary Syndrome during Hajj period. Design: A quasi-experimental design (pre/posttest non-equivalent control group) was employed. Sample: A convenience sample of 100 adult male and female patients was divided into two groups one of study group who receiving nursing instruction and control group who receiving hospital care. Tools: Three tools were utilized:(1) Demographic and Medical Data Form, and (2) Lifestyle Modification Tool, and (3) Acute Coronary Syndrome (ACS)-related complications. Setting: The study was conducted in cardiac ward in King Abdullah Medical City, Holy Makkah, Saudi Arabia. Results: The finding revealed that the mean ages of the study and control group 61.86 +12.76. and 59.36+12.9 years respectively. Statistically significant differences were found in lifestyle knowledge level observed between Study group and the control group. (F=72.171-p=0.000). Besides, there was a negative correlation between total knowledge score and complication rate of the study sample r=.0.33 at p= 0.01. Conclusion: The current study concluded that effective nursing instructions is very important in improving patient’s knowledge regarding ACS management and reduces complication rate. Recommendation: Based on the study findings, it is recommended to integrate the Illustrative booklet related to Lifestyle patient knowledge into routine nursing care for patients with ACS. furthermore, continuous training should be provided for health care staff to enhance their instructional skills.