This report describes a 63 year-old man who suffered an acute myocardial infarction after carbon monoxide exposure. When evaluated in the Emergency Room the patient was completely conscious and did not experience any chest pain. The electrocardiogram showed non-specific T wave abnormalities in inferolateral leads. The only sign consistent with a possible myocardial involvement was a slight increase in serum CPK. The electrocardiogram taken 12 hours later revealed a Q-wave inferior myocardial infarction, and CPK levels showed a typical elevation in the following 24 hours. The coronary angiography, performed about two weeks after admission, documented multiple obstructions in the main coronary branches. In the presence of a reduced coronary reserve, the onset of a prolonged myocardial ischemia might have been secondary to a decreased oxygen transport capacity of the blood, which lead to a decreased amount of oxygen available to the tissues. According to their experience, the authors emphasize the importance of a careful electrocardiographic and enzymatic monitoring of all patients in the first hours after CO exposure, because the typical chest pain may be absent.