I am assuming that the left sided coronary artery is just small as you describe, and that it is not severely diseased and therefore small-appearing. I am assuming that you also do not have some congenital anomaly with your coronary arteries. If it is just that you were born with a small left sided artery and there is no part of your heart that does not need more blood, then there is no problem. You do want to make sure you take good care of your high blood pressure and diabetes (and high cholesterol if that applies) to reduce your chances of developing coronary artery disease.