Background: Myocardial infarction is the leading cause of global morbidity and mortality. More than 3 million individuals develop ST-segment elevation myocardial infarction yearly. Timely management of myocardial infarction is curious to improve survival and outcomes. Aim: To assess knowledge and prehospital delay for elderly patients presenting with acute myocardial infarction undergoing primary percutaneous coronary intervention. Research design: Descriptive research. Setting: The study was conducted in cardiac catheterization and coronary care unit at Assuit University Heart Hospital. Sample: A convenient sample of 208 patients. Tools, Tool I: Demographic and medical data questionnaire. Tool (II): A questionnaire for assessing patient's knowledge about myocardial infarction was collected for all patients. Results: 208 patients were included (71.6% males, age 70.1±4.4). 65.9% of patients had poor knowledge about myocardial infarction (< 50%). Also, (85.9%) of patients with poor knowledge reached hospital after more than 6hours from symptoms onset. However, 44.4% of patients with fair or good knowledge reached hospital in less than 2hours. Patients with longer prehospital delays had longer hospital stay and more complications (p-value = 0.045) compared with those who presented earlier. Conclusion: The study underscores the critical role of patient knowledge about myocardial infarction in reducing prehospital delay and its impact on hospital stay and clinical outcomes. Recommendation: Organize regular awareness programs to educate elderly people about myocardial infarction symptoms and seek prompt medical treatment.