73-year-old man with peripheral vascular disease and significant smoking history experienced the acute onset of chest pain, shortness of breath, and dizziness. Shortly following symptom onset, he collapsed and sustained a small head laceration. Upon arrival to the emergency department, the patient was found to be unresponsive, bradycardic, and hypotensive. Heart rate was 44/minute and regular; systolic blood pressures were in the seventies. He was immediately intubated. The initial electrocardiogram (ECG) demonstrated up to 5 mm ST segment elevation in leads V1 through V4 suggestive of an acute anterior myocardial infarction (MI) (Fig 1). What was the most likely site of coronary occlusion? The ECG in Figure 1 demonstrates atrial fibrillation with third-degree AV block, a slow junctional escape rhythm, and a premature ventricular complex. Note the absence of P waves and the fine baseline undulations characteristic of atrial fibrillation, as well as a regular narrow complex rhythm without distinct P waves diagnostic of a junctional rhythm. The QT interval is slightly prolonged. There is also prominent ST elevation in leads V1-V4 and subtle ST elevation in leads III, aVF, as well as ST depression in lateral leads I, aVL, V5 and V6. The frontal axis is noted to be rightward. In patients with acute myocardial infarction, the combination of early onset atrial fibrillation, AV block and a junctional escape rhythm almost always signifies an inferior MI due to occlusion of the proximal right coronary artery (RCA), or less commonly, occlusion of the left circumflex coronary artery (LCX). 1 The sinus node artery that supplies much of the atrial myocardium comes off from the proximal RCA or LCX. The dominant artery (RCA in 85% and LCX in 10% of individuals) supplies the inferior wall of the left ventricle. It also gives off the AV node artery. Occlusion of the proximal RCA or LCX in an inferior MI, therefore, may cause atrial ischemia resulting in early onset atrial fibrillation, and AV