Background: Carbon monoxide (CO) is one of well known chemical asphyxiants which can cause tissue hypoxia with prominent neurologic and cardiovascular injury. Exposure to CO can cause global left ventricular (LV) dysfunction or LV dysfunction with regional wall motion abnormalities. However, the presence of LV dysfunction can be masked, because these patients are usually disoriented as a result of CO poisoning. Thus we prospectively evaluated the echocardiographic findings in the consecutive patients with CO exposure. Materials and Methods: We included total patients with CO exposure in the emergency room. We analyzed their clinical and echocardiographic patterns. If the patient showed LV systolic dysfunction (LV ejection fraction (LVEF) < 50%), the follow up echocardiography was done until LV function will be normalized. Results: From January 2009 to May 2010, we included total twenty patients (13 males, mean age 50.6 짹 17.9 years) with CO exposure. Twelve patients (60%) showed LV systolic dysfunction (mean LV ejection fraction was 34.7 짹 8.1% (range 23 ~ 47%). Of them with LV systolic dysfunction, 8 showed global hypokinesia and 4 with regional wall motion abnormalities. Patients with LV systolic dysfunction were associated with severe CO poisoning, pulmonary edema, and higher concentration of N-terminal BNP and troponin I level. Nine patients with LV systolic dysfunction showed decreased mentality (4 drowsy, 4 stuporous and 1 comatous). They showed complete recovery of LV systolic function with conventional treatment after 2~7 days. Conclusion: CO poisoning can cause transient LV systolic dysfunction. The presence of cardiac toxicity should be identified with prompt echocardiographic examination.