Left main stem stenosis in the unstable patient--forewarned is forearmed.

Recognition of clinical and electrocardiographic features suggestive of significant left main coronary artery disease is important, particularly in patients presenting with an acute coronary syndrome. These include hemodynamic instability and widespread ST segment depression, which are well known. In addition, ST segment elevation in lead aVr, a less recognised finding associated with severe left main disease, may be present.