Acute anterolateral MI is recongnized by ST segment elevation in leads I, aVL and the precordial leads overlying the anterior and lateral surfaces of the heart (V3 - V6). Generally speaking, the more significant the ST elevation , the more severe the infarction. There is also a loss of general R wave progression across the precordial leads and there may be symmetric T wave inversion as well. Anterolateral myocardial infarctions frequently are caused by occlusion of the proximal left anterior descending coronary artery, or combined occlusions of the LAD together with the right coronary artery or left circumflex artery. Arrythmias which commonly preclude the diagnosis of anterolateral MI on ECG and therefore possibly identify high risk patients include right and left bundle branch blocks, hemiblocks and type II second degree atrioventricular conduction blocks.