,LEFT MAIN CORONARY ARTERY:,  The left main coronary artery has a posteriorly positioned take-off from the valve cusp, with a patent ostium, and it has an extramural (non-malignant) course. 
,LEFT MAIN CORONARY ARTERY : , The left main coronary artery has a posteriorly positioned take - off from the valve cusp , with a patent ostium , and it has an extramural ( non - malignant ) course .