The electrocardiographic diagnosis of acute myocardial infarction in patients being paced by unipolar pacemakers has been made possible. The technique of shorting out the pacemaker is simple and can be performed repeatedly at the bedside. Two patients were clinically suspected of having acute myocardial infarction. Electrocardiograms taken in the absence of pacemaker stimulus distortion of the QRS complex confirmed the diagnosis in one patient and helped rule out the diagnosis in the other.