Objective: The cardiac arrhythmias detected by ECG monitoring in acute myocardial patients. Subject and method: A cross sectional study was done on 30 acute myocardial infarction hospitalized in No.108 Military Central Hospital in 2013. Result: The results as followed: The prevalence of premature supraventricular complex and atrial fibrillation were found higher on a monitor than on conventional ECG (13.3 percent vs 3.3 percent), the prevalence of premature ventricular complex was detected on first 2 days as 40 percent, 20 percent, which were higher than on conventional ECG. Ventricular tachycardia was found on monitor, but was not recorded on ECG. Conclusion: In clinical practice, it is important to monitor patients with acute myocardial infarction to detect arrhythmias.