PLE-796

A 57-year-old stockbroker is brought to the cardiac catheterization laboratory emergently after evaluation in the emergency department has determined that he is suffering from an acute myocardial infarction. During the catheterization, he is found to have inadequate blood flow in the artery that runs aside the great cardiac vein in the anterior interventricular sulcus of the heart. This is most likely an acute occlusion of the: