Objective: The assessment of short duration early clarithromycin treatment on major cardiac events in acute coronary syndrome patients Methods: One hundred and thirteen patients with acute coronary syndrome had been enrolled in the study in a prospective manner. Fifty-seven of 113 patients received peroral clarithromycin 1g/day for 14 days in addition to standard therapy. The remaining 56 patients were considered as control group. The treatment and control groups had similar major cardiac risk factors such as diabetes, hypertension, dyslipidemia and smoking habits. The occurrence of unstable angina pectoris, non-ST elevation myocardial infarction and ST elevation myocardial infarction was comparable in both groups. The use of thrombolytic therapy and glycoprotein IIb/IIIa receptor blockers administration was also similar in both groups. The patients were followed for major cardiac events for 6 months. Results: During the follow-up, no difference was observed between groups in the occurrence of unstable angina pectoris, myocardial infarction, the need for revascularization with percutaneous coronary intervention or cardiac surgery and cardiac death. We observed a reduction of myocardial infarction and cardiac death occurrence and an increase in the necessity of percutaneous interventions in the treatment group even though this difference did not reach statistical significance. Conclusion: No benefit of short duration early clarithromycin therapy was observed in the occurrence of major cardiac events in acute coronary syndromes. Studies with longer treatment and follow-up period using different antibiotics are necessary to elucidate the possible effect of antibiotics on major cardiac events in patients with acute coronary syndrome.